JP3740155B2 - Method for predicting acicular ferrite transformation rate of weld metal part, and method for predicting morphology of acicular ferrite - Google Patents

Description

  The present invention relates to a method for predicting an acicular ferrite transformation rate (area ratio) in a weld metal part after welding in general welding such as arc welding, laser welding, and electron beam welding, and a form of the acicular ferrite. It relates to the method of prediction.

  In recent years, various welding methods have been applied to weld building structures such as ships, steel frames, bridges, etc., but the weld metal part after welding (which means the whole weld metal part or a part thereof) Predicting the mechanical properties (including both) in advance is important in obtaining a weld metal part with the desired properties. The mechanical properties of the weld metal part are determined by the composition of the weld metal part (composition when the base material used and the welding material are melted to form a weld metal) and the structure. There are few methods for predicting mechanical properties taking into account the organization.

  For example, Patent Documents 1 to 3 below all relate to a technique for predicting the mechanical properties of a weld metal part, but the base material component, welding conditions, weld metal composition, etc. are considered, but the structure is considered. It has not been.

  Among these, Patent Document 1 proposes a technique for predicting the composition of the weld metal from the base material component, the welding current, the welding voltage, the welding speed, the wire component, and the flux component with respect to the submerged arc welding.

  In Patent Document 2, the relationship between the composition and thermal history of the weld metal and / or base material heat-affected zone and the mechanical properties of the weld metal and / or base material heat-affected zone is determined in advance, and (i ) Welding condition parameters such as base metal shape and groove shape, (ii) thermal conductivity and density of weld metal based on database of weld metal components, and (iii) heat of base metal based on database of base metal components Using the conductivity and density, the composition and thermal history of the weld metal and / or base metal heat-affected zone are determined by calculation, the composition and heat history determined by the calculation, and the previously determined weld metal and / or A method for predicting the mechanical properties of a weld metal and / or base metal heat affected zone by collating the composition and thermal history of the base metal heat affected zone with the mechanical properties is disclosed.

  Further, Patent Document 3 discloses a cooling rate when welding is performed under various welding conditions using a specific base material and a specific wire, and mechanical properties of the reheated part and the original part of the weld metal. And the area ratio of the cross section of the reheated part and the original part when welding is performed under various welding conditions using the specific base material and the specific wire. , The relationship between the cooling rate calculated by the plate thickness and the like when welding using the specific base material and the specific wire, and the mechanical characteristics, and the welding conditions and the area of the reheated part and the original part A method for predicting the mechanical properties of a weld metal by checking the relationship with the ratio is disclosed.

  As described above, all of the above Patent Documents 1 to 3 are prepared by previously creating a database of relationships between base material components, welding conditions, weld metal composition, and the like, and predicting base material components and welding conditions based on the database. Yes, no consideration is given to the structure governing the mechanical properties of the weld metal. For this reason, there is a problem that the accuracy of predicting the mechanical characteristics is lowered when the base material component to be used and the welding conditions are changed.

  On the other hand, among the structures constituting the weld metal part, in particular, the acicular ferrite is a very fine structure, and is an important structure for determining the mechanical properties of the weld metal part. Therefore, it is a method capable of predicting the acicular ferrite transformation rate (acicular ferrite fraction) in the weld metal portion analytically with high accuracy, and a method capable of predicting the mechanical properties of the weld metal portion based on the method. Offering is anxious.

  Here, the structure constituting the weld metal part will be briefly described. FIG. 1 is a schematic diagram of a structure constituting a weld metal part, in which 1 is an allotrimorphic ferrite (generally called a grain boundary ferrite) and 2 is a Widmannstatten ferrite having an acicular structure. (Widmanstatten ferrite), 3 is acicular ferrite, 4 is pearlite, and 5 is a microphase.

  As shown in FIG. 1, the weld metal part is composed of a combination of allotriomorphic ferrite 1, Widmanstatten ferrite 2, acicular ferrite 3, pearlite 4, and microface 5. Varies depending on each component of the base material and welding material used, welding conditions, and the like. Of these, the area of the acicular ferrite 3 is enlarged as shown in FIG. 1B, and the pearlite 4 and the microface 5 are generated in the gap of the acicular ferrite 3.

  Among the above-mentioned structures, allotriomorphic ferrite and Widmanstatten ferrite are described in Bhadeshia reference 1 (HKDH Bhadeshia, L.-E. Sevensson: Mathematical Modeling of Weld Phenomena, The Institute of Materials (1993), p109- 178) and reference 2 by Ichikawa et al. [Kazutoshi Ichikawa, HKDH Bhadeshia (Mathematical Modeling of Weld Phenomena 4, IOM Communications (1998), p302-320)].

However, a structure prediction model of acicular ferrite 3 has not been provided yet. For example, the above-mentioned reference 1 only discloses the following equation as an equation for indirectly calculating the acicular ferrite transformation rate (Va).
Va = 1-Vα-Vw-Vm
(Where Va is the fraction of acicular ferrite,
Vα is the allotriomorphic ferrite fraction,
Vw is the Widmanstatten ferrite fraction,
Vm means the microface fraction, respectively. )

  Vα, Vw, Vm are calculated in advance based on the premise that “the structure is composed of allotriomorphic ferrite, Widmanstatten ferrite, microface, and acicular ferrite”. In addition, the acicular ferrite fraction (Va) is indirectly calculated by subtracting these totals. Therefore, in order to calculate the acicular ferrite fraction based on the above-described method, it is necessary to calculate the structure other than the acicular ferrite. Moreover, the acicular ferrite fraction calculated by the above equation does not necessarily match the actual measurement value. As shown in FIG. 1B described above, in practice, pearlite is formed in the gap between the acicular ferrites in addition to the microface, but the above formula does not take into account the structure concerned. is there.

  Therefore, the present inventors have intensively studied paying attention to the structure of the weld metal part that has not been considered in the past in order to provide a method capable of accurately and easily predicting the mechanical characteristics of the weld metal part. In general, the weld metal portion formed by welding is repeatedly heated and cooled for each pass from the first weld pass to the final weld pass. Therefore, depending on the welding conditions, a crystallized substance mainly composed of oxide [(Mn, Ti , Si) O, (Al, Mn) O, etc.], and the transformation structure (ferrite, pearlite, martensite, bainite, acicular ferrite, etc.) changes greatly. Because it was not done.

  As a result, the present inventors have predicted the structure of the weld metal part, and based on this, have found a method capable of accurately predicting the mechanical properties of the weld metal part, and have already filed an application (Patent Literature). 4).

  The above method divides a welded portion into a plurality of mesh regions, and for each mesh region, (i) mesh region temperature calculation (base material component, wire component or unit per unit time until the end of the final welding pass) A method of calculating the temperature history from the first welding pass to the final welding pass by sequentially obtaining the mesh region temperature after the passage of the unit time based on the weld metal composition and welding conditions before the passage of time), (ii) welding Metal composition calculation (based on the base metal component, wire component, shield gas component or weld metal composition before the unit time elapses and mesh region temperature after the unit time elapses until the end of the final welding pass. (Method of obtaining weld metal composition after unit time), (iii) Transformation structure calculation (Method of obtaining transformation structure information including the fraction of transformation structure in mesh region) After each calculation, based on the transformation structure information after completion of the final welding pass in each mesh area, the material calculation for predicting the material of the weld metal part from the relationship between the structure and the material obtained in advance by actual measurement Is to do. According to the above method, the composition, crystallized material, and temperature history of the weld metal, which are important determinants in predicting the mechanical properties of the weld metal, [particularly, the “last heating” that most affects the final structure. By performing the transformation structure calculation of (iii) described above only for the “cooling process” (to be described later), the calculation load is reduced and the characteristics can be predicted quickly.] Compared with the conventional method, the prediction accuracy of the weld metal part can be increased.

Further, in Patent Document 4, the transformation of acicular ferrite (AF) is based on the following equation by using ferrite grain information and acicular ferrite grain information as transformation structure information in the transformation structure calculation of (iii). A method for determining the fraction and the average particle size of the acicular ferrite is also disclosed.
AF fraction = 1−expΣ (−k · Iaf (T) · αaf (T) · Δt ^1/2 )
AF average particle diameter = {ΣIaf (T) · αaf (T) · Δt} / ΣIaf (T)
Where k is a constant,
Iaf (T) is the nucleation rate of AF at temperature T,
αaf (T) is the AF growth constant at temperature T,
Δt is a minute time,
The accumulated time is calculated from the start temperature of the acicular ferrite transformation to the martensite transformation.
This is the time until the state start temperature or the pearlite transformation start temperature is reached.

  However, according to the above method, the values of constants k, Iaf (T), and αaf (T) vary depending on the composition and temperature of the weld metal. It must be calculated from the relational expression obtained by regression analysis, and it is necessary to construct a database in advance.

As described above, the above method can provide a method for accurately predicting the structure of the weld metal part for the first time, and is very useful in that it also discloses a means for predicting the acicular ferrite transformation rate. However, there is a disadvantage that it is necessary to create a database in advance by experiments.
Patent No. 2850773 (Claims) JP 2002-79375 A (Claims) JP 2002-178147 A (Claims) JP 2004-4034 A (Claims)

The present invention has been made based on the above circumstances, and an object thereof is to provide a method capable of accurately and easily predicting the acicular ferrite transformation rate of the weld metal part and the form of the acicular ferrite. It is in. The acicular ferrite (AF) in the present invention means a plate-like acicular ferrite, and is represented by the product of the side area A (m ² ) and the plate thickness W (m).

The method for predicting the acicular ferrite transformation rate (fraction) of the weld metal part according to the present invention that has achieved the above object (hereinafter sometimes referred to as “AF transformation rate prediction method”) is a single pass or A method for predicting the acicular ferrite transformation rate of a weld metal part formed by multiple passes,
(A) Basic information calculation means for calculating the composition of the weld metal part, the crystallized substance information, and the cooling temperature history from the first welding pass to the final welding pass based on the respective components of the base material and the welding material and the welding conditions. When,
(B) Based on the transformation start temperature and transformation end temperature of the acicular ferrite calculated by thermodynamic calculation, predict the acicular ferrite transformation rate of the weld metal at the end of the final welding pass. Including rate prediction means,
The above (b) divides the cooling temperature history of (a) into minute times, and sequentially calculates the acicular ferrite transformation rate X _AF (T) at the temperature T for each minute time, thereby completing the final welding pass. Is to predict the acicular ferrite transformation rate of the weld metal part at the time,
The shape of the acicular ferrite (AF) is represented by the product of the side area A (m ² ) and the plate thickness W (m).
The X _AF (T) has a gist where it is calculated based on the following formula (1).
X _AF (T) = 1−exp (−A _T × P _T × W _T ) (1)
_Where X _AF (T) is the AF transformation rate at temperature T;
A _T is the AF side area at temperature T (m ² );
P _T is the density of AF at temperature T (pieces / m ³ );
W _T is the plate thickness (m) of AF at temperature T;
W _T = α × t ^1/2 ,
α is assumed when AF is transformed in para-equilibrium.
Parabolic rate constant;
t is the holding time at temperature T (seconds)
Means
The (A _T × P _T ) is represented by the following formula (2).
(A _T × P _T ) = − 1.699 × 10 ⁵ −7.506 × 10 ² × (dGγ → α)
(2)
Where (dGγ → α) is from austenite to ferrite at temperature T
Driving force of non-diffusion transformation when transforming to (J / mol)
It is.

  Here, as the cooling temperature history of the above (a), the temperature history at the time of cooling from the highest temperature in the last heating and cooling process in which heating is performed at a temperature higher than the temperature at which the austenite transformation is completed in multi-pass welding is used. Recommended.

In carrying out the above (b) “Accurate ferrite transformation rate prediction means for weld metal”, first, (b-1) the temperature at which the acicular ferrite starts transformation (transformation calculation start temperature) is determined. Then, (b-2) the transformation rate of the acicular ferrite is calculated from the transformation calculation start temperature (specifically, the temperature at each minute time when the cooling temperature history is divided into minute times). The acicular ferrite transformation rate X _AF (T) at T is sequentially calculated), and the carbon concentration Cγ in the untransformed γ corresponding to the X _AF (T) is obtained. ) Is defined as the temperature at which the acicular ferrite finishes transformation (transformation calculation end temperature), and the calculated value up to the transformation calculation end temperature is the acicular ferrite transformation rate of the weld metal part. X _AF .

  Among these, “transformation start temperature of acicular ferrite (transformation calculation start temperature)” can be calculated based on the composition of the weld metal part and the driving force (dGγ → α) of non-diffusion transformation by thermodynamic calculation. Specifically, the temperature is the temperature at which the driving force of the non-diffusion transformation is 400 to 800 J / mol.

On the other hand, "transformation end temperature of acicular ferrite (transformation end temperature)" is determined based on the composition of the weld metal part and the cooling temperature history,
Temperature at which carbon content Cγ in untransformed austenite and carbon content C (Acm) at Acm point intersect; or Ms point, where T0 is the higher temperature, T0 (T0-50 ° C) range And

Further, the form of the acicular ferrite of the weld metal part according to the present invention that can achieve the above object (the “form of the acicular ferrite” in the present invention is specifically the side area A (m ² ) and the plate thickness W). A method for predicting each side area and plate thickness in a plate-like acicular ferrite having (m); and further intended the density P (pieces / m ³ ) of acicular ferrite having such a shape ( Hereinafter, it may be referred to as “AF form prediction method”) is a method of predicting the acicular ferrite transformation rate of a weld metal part formed by a single pass or multiple passes,
(A) Basic information calculation means for calculating the composition of the weld metal part, the crystallized substance information, and the cooling temperature history from the first welding pass to the final welding pass based on the respective components of the base material and the welding material and the welding conditions. When,
(C) includes a method for predicting the shape of the acicular ferrite of the weld metal portion, which is calculated based on the basic information calculation means of (a), and predicts the shape of the acicular ferrite at the end of the final welding pass,
The shape of the acicular ferrite (AF) is represented by the product of the side area A (m ² ) and the plate thickness (m).
The above (c) divides the cooling temperature history of (a) into minute times, and the AF side area A _T and (A _T × P _T ) at the temperature T for each minute time (where P _T is , Which is the density of AF at temperature T), the AF side area A (m ² ) of the weld metal portion at the end of the final welding pass, the plate thickness W (m) of the AF, and the AF Density P (pieces / m ³ ), respectively,
The _AT is calculated based on the following formula (3):
The (A _T × P _T ) has a gist where it is calculated based on the following formula (2).
A _T = β × P _T ^-2/3 (3)
Where A _T is the AF side area at temperature T (m ² );
β is a proportionality constant;
P _T is the density of AF at temperature T (pieces / m ³ )
It is.
(A _T × P _T ) = − 1.699 × 10 ⁵ −7.506 × 10 ² × (dGγ → α)
(2)
Where (dGγ → α) is from austenite to ferrite at temperature T
It is the driving force (J / mol) of the non-diffusion transformation when transforming.

  Among these, in the above formula (3), β may be a weld metal part actually made using a wire and a base material, and an experimental value obtained based on the above formula (3) may be adopted. Experimental values may be adopted. Or you may employ | adopt the calculated value ((beta) = 1-3, Preferably 1.5 or more, 2.5 or less) derived | led-out based on our basic experiment.

  Here, as the cooling temperature history of the above (a), the temperature history at the time of cooling from the highest temperature in the last heating and cooling process in which heating is performed at a temperature higher than the temperature at which the austenite transformation is completed in multi-pass welding is used. Recommended.

Further, in carrying out the above-mentioned (c) “Acicular ferrite shape prediction means of weld metal part”, first, (c-1) the temperature at which the acicular ferrite starts transformation (transformation calculation start temperature) was determined. (C-2) Calculate the form of acicular ferrite from the transformation calculation start temperature [specifically, the temperature T at each minute time when the cooling temperature history is divided into minute times. The side areas A _T and (A _T × P _T ) (where P _T is the density of AF at the temperature T) are sequentially calculated] and the transformation of the acicular ferrite The carbon concentration Cγ in the untransformed γ corresponding to the rate is obtained, and the temperature when this Cγ satisfies the transformation end condition (described later) is the temperature at which the acicular ferrite finishes the transformation (transformation calculation end temperature) The calculated values up to the transformation calculation end temperature are defined as the side area A, the plate thickness W, and the density P of the acicular ferrite of the weld metal part, respectively.

  Among these, “transformation start temperature of acicular ferrite (transformation calculation start temperature)” can be calculated based on the composition of the weld metal part and the driving force (dGγ → α) of non-diffusion transformation by thermodynamic calculation. Specifically, the temperature is the temperature at which the driving force of the non-diffusion transformation is 400 to 800 J / mol.

On the other hand, "transformation end temperature of acicular ferrite (transformation end temperature)" is determined based on the composition of the weld metal part and the cooling temperature history,
Temperature at which carbon content Cγ in untransformed austenite and carbon content C (Acm) at Acm point intersect; or Ms point, where T0 is the higher temperature, T0 (T0-50 ° C) range And

  According to the method for predicting the acicular ferrite transformation rate of the present invention, the `` acicular ferrite transformation rate of the weld metal part '', which could not be predicted in the past, is measured ± even if the raw material components and welding conditions are changed. It is possible to provide an extremely accurate transformation rate prediction method that can predict within an error range of 10% or less.

  Furthermore, according to the method for predicting the shape of the acicular ferrite of the present invention, the “form of the acicular ferrite in the weld metal part (specifically, the side area, the plate thickness, the number of plate-like acicular ferrite) that could not be predicted in the past. "Can be predicted with high accuracy even if welding is performed by changing raw material components and welding conditions. Specifically, the side area of the plate-like acicular ferrite is in the range of 75% ≦ (predicted value / measured value) ≦ 150%; the plate thickness of the plate-like acicular ferrite is 75% ≦ (predicted) Value / actual value) ≦ 150%: The number of the plate-like acicular ferrite can be predicted within a range of 75% ≦ (predicted value / actual value) ≦ 150%.

  Furthermore, if the prediction method mentioned above is used, it can fully be expected that the mechanical properties of the weld metal part are predicted with high accuracy.

  As described above, the present inventors are diligently studying to provide a method capable of directly and accurately predicting the transformation rate of acicular ferrite among the structures constituting the weld metal part. As a result, first, the method of Patent Document 4 is disclosed. Further, after that, it succeeded in expressing the acicular ferrite transformation rate as a function of the temperature T and the crystallization information N of the weld metal part, and has been filed separately (Japanese Patent Application No. 2003-58861, hereinafter “ It may be referred to as “prior invention”).

The prediction method of the above "prior application invention"
(A) Basic information calculation means for calculating the composition of the weld metal part, the crystallized substance information, and the cooling temperature history from the first welding pass to the final welding pass based on the respective components of the base material and the welding material and the welding conditions. When,
(B) Based on the transformation start temperature and transformation end temperature of the acicular ferrite calculated by thermodynamic calculation, predict the acicular ferrite transformation rate of the weld metal at the end of the final welding pass. Including rate prediction means,
Based on the following formula (1), the acicular ferrite transformation rate X _AF (T) at temperature T is calculated, and the cooling temperature history of (a) is divided into minute times (Δt), and the minute times (Δt) By sequentially calculating X _AF (T) every time and adding them (addition rule), the “acicular ferrite transformation rate of the weld metal part” after welding is predicted.
X _AF (T) = 1−exp (−A ₀ × α × t ⁿ ) (1)
However, n = 0.3-0.7
_Where X _AF (T) is the transformation rate of acicular ferrite at temperature T
A ₀ is the nucleation constant,
α is when acicular ferrite transforms in para-equilibrium
Parabolic rate constant when assumed,
t is the holding time (seconds) at temperature T,
n is an index representing the time dependence of the acicular ferrite transformation rate
It is.

Here, the process of reaching the method of the “prior application invention” will be briefly described. The inventors of the present invention described, “In order to calculate the acicular ferrite transformation rate of the weld metal part, first, the acicular ferrite Based on the viewpoint that “the nucleation / growth state and the shape of the acicular ferrite need to be determined”, the test material of the weld metal part was subjected to a basic heat treatment simulator shown in FIG. As a result, the acicular ferrite transformation rate X _AF (T) when held at the temperature T is a function A ₀ (N, N) of the crystallization information N of the weld metal part calculated by the step (a) and the temperature T. It was found that it was calculated based on T), and the “prior invention” was completed.

  According to the method of the “prior application invention”, the “acicular ferrite transformation rate of the weld metal part” is predicted within an error range within ± 5% of the actual measurement value even if welding is performed by changing the composition of the raw materials and the welding conditions. We were able to provide an extremely accurate prediction method that could be done.

However, even in the above-mentioned “prior application invention”, in the same manner as in Patent Document 4 described above, in calculating the acicular ferrite transformation rate X _AF (T) at the temperature T, a database of A ₀ (N, T) in advance is calculated. Have the inconvenience of having to create.

Therefore, in the present invention, in order to provide a method that can more easily predict the transformation rate of acicular ferrite more accurately without preparing a database in advance, further research is repeated based on the method of the “prior invention”. I came. As a result, in the prediction method of the “prior invention” [a method including (a) basic information calculation means and (b) acicular ferrite transformation rate prediction means of a weld metal part] As a formula that can easily calculate the acicular ferrite transformation rate X _AF (T) at temperature T without modifying the means and constructing a database, a factor (side area A) related to the form of acicular ferrite And succeeded in deriving the formula specified by the plate thickness W and the density P). And the basic information calculation means of (a) in the above-mentioned "prior application invention" and the "acicular ferrite transformation rate prediction means of the weld metal part" calculated based on the above formula (1) specified in the present invention. As a result, it was found that the acicular ferrite transformation rate of the weld metal part can be predicted more easily and accurately by integrating using the “addition rule” in the same manner as the “prior application invention”.

Furthermore, in predicting the form of the plate-like acicular ferrite (side area A, plate thickness W, and density P), “when the acicular ferrite is generated from the nucleation site, the major axis L and the minor axis of the acicular ferrite Assuming that W is determined by collision with other acicular ferrite, both the major and minor axes are proportional to the average distance of the nucleation site. The above formula (3) of the area _AT and the density P _{T of the} acicular ferrite at the temperature T was derived. And, in the formula (3) and the formula (1) related to the transformation rate X _AF (T) of the acicular ferrite at the temperature T, if the formula (2) represented by the product of _AT and _PT is used, The inventors have found that the side area A, the plate thickness W, and the density P of the AF of the weld metal part can be easily and accurately predicted, and the present invention has been completed.

  First, a method for predicting the acicular ferrite transformation rate of a weld metal part according to the present invention, including the series of basic experiments described above, will be described in detail with reference to the drawings. FIG. 3 is a flowchart showing a procedure for carrying out the method of the present invention, which is prepared assuming a welding operation represented by arc welding by a single or a plurality of passes using a base material and a welding material. is there. Specifically, it is implemented using a material prediction computer in which a program for executing each means is stored in a storage device.

(1) About prediction method of acicular ferrite transformation rate of weld metal part
(A) Basic information calculation means The above (a) is based on the respective components of the base material and the welding material, and the welding conditions, the composition of the weld metal part, the crystallized information, and the cooling from the first pass to the final welding pass. Basic information calculation means for calculating the temperature history (represented as “basic information calculation means” in FIG. 3). This step is the same as the step (a) of the “prior application invention”.

  Among these, the welding material which is a raw material includes a solid wire, a cored wire, and the like, and further, a welding material for submerging using a solid wire and a flux together is exemplified. The welding conditions include welding current, welding voltage, welding speed, pass-to-pass temperature (weld zone allowable temperature when welding of the next pass is started), base metal shape (plate thickness), groove shape, welding The length, the number of passes, etc. can be mentioned, and further, two-dimensional information such as pass welding time (welding time required per pass = welding length / welding speed) calculated from these data is also included.

  Based on the respective components of the base material and the welding material and welding conditions, (i) the composition of the weld metal part, (ii) crystallized substance information (for example, the composition of the crystallized substance, the average particle diameter, and the number per unit area) ), And (iii) a cooling temperature history from the first welding pass to the final welding pass (hereinafter sometimes simply referred to as “cooling temperature history”). This is because these are important basic parameters for accurately predicting the acicular ferrite transformation rate of the weld metal part.

  The method for calculating the above (i) to (iii) is not a characteristic part of the present invention, and a known method can be adopted. For example, the methods described in Patent Documents 1 to 3 described above may be referred to. . Further, it is possible to calculate based on the method of Patent Document 4 and the details thereof are as described above. To summarize, the base material component, the wire component, and the welding conditions are input to the material prediction calculator. , A database stored in a storage device [investigated in advance by experiments, etc., specifically, (a) composition (base material, weld metal), liquidus temperature, solidus temperature, Phase diagram database showing the relationship between the temperature at which austenite transformation ends in the heating process (temperature at which austenite begins to form), the temperature at which ferrite transformation ends in the cooling process, etc. (b) Crystallized products that crystallize from the weld metal composition Type, melting and heating temperature, solidification time from the same temperature to the solidus temperature, crystallized material database showing average particle size and amount of crystallized (number per unit area), etc.] Calculation should be.

  Of the basic information (i) to (iii) calculated in this way, the cooling temperature history of (iii) is the temperature history of the weld metal part calculated according to the method described above (from the first welding pass to the final). It is determined based on the history of heating / cooling repeated for each pass over the welding pass). In the present invention, as in the above-mentioned Patent Document 4, as the above cooling temperature history, the last heating / cooling process (hereinafter referred to as “the last heating / cooling process”) that is heated to a temperature higher than the temperature at which the austenite transformation is completed in multi-pass welding. It is recommended to use a temperature history during cooling from the maximum temperature (hereinafter sometimes referred to as “cooling rate after the last austenite transformation”). This is because calculating the entire temperature history of the weld metal part and calculating the acicular ferrite transformation rate of the weld metal part based on all of these temperature histories results in an excessive load; on the other hand, the transformation of the acicular ferrite The cooling temperature history is the largest contributor to the process, and the most significant effect is considered to be the "last heating and cooling process". Therefore, the "cooling rate after the last austenite transformation" in the "last heating and cooling process" This is because even if the acicular ferrite transformation rate of the weld metal part is calculated based on the above, a high degree of prediction accuracy is maintained.

(B) Means for predicting acicular ferrite transformation rate of weld metal part The above (b) is based on the transformation start temperature and transformation end temperature of acicular ferrite calculated by thermodynamic calculation, and the weld metal part at the end of the final welding pass. The acicular ferrite transformation rate is predicted, and in FIG. 3, this is expressed as “acoustic ferrite transformation rate prediction means for weld metal part”.

Specifically, in carrying out the above (b), first, (b-1) the temperature at which the acicular ferrite starts transformation (transformation calculation start temperature) is determined, and (b-2) the transformation calculation is started. The transformation rate of acicular ferrite is calculated from the temperature (specifically, the acicular ferrite transformation rate X _AF (T) at the temperature T for each minute time when the cooling temperature history is divided into minute times. In addition, the carbon concentration Cγ in the untransformed γ corresponding to the X _AF (T) is obtained, and the temperature at which this Cγ satisfies the transformation end condition (described later) is determined as the acicular ferrite. There defined as the temperature at which to end the transformation (transformation calculation end temperature), the calculated value to the transformation calculated end temperature, the acicular ferrite transformation ratio X _AF of the weld metal portion.

  Hereinafter, the above (b) will be described in detail with the background of the basic experiment.

(B-1) Determination of transformation start temperature of acicular ferrite First, the temperature at which acicular ferrite starts transformation is determined. Thereby, the temperature at which the calculation of the acicular ferrite transformation rate is started (transformation calculation start temperature) is determined.

  The transformation calculation start temperature of the acicular ferrite is calculated based on the composition of the weld metal part and the driving force (dGγ → α) of the non-diffusion transformation by thermodynamic calculation. Specifically, the driving of the non-diffusion transformation The temperature when the force (dGγ → α) reaches 400 to 800 J / mol. In the present invention, “the transformation start temperature of the acicular ferrite is synonymous with the temperature at which the bainite transformation starts”, and “the driving force of the non-diffusion transformation (dGγ → “The temperature when α) is 400 to 800 J / mol” is also adopted in the present invention.

  The method for determining the transformation calculation start temperature of acicular ferrite described above will be described in more detail with reference to FIG. FIG. 4 is a graph showing a method for determining the transformation calculation start temperature and transformation calculation end temperature (described later) of acicular ferrite. Of these, FIG. 4 (a) shows the horizontal axis representing time [holding time (transformation time (transformation time)]. )], The cooling temperature history when the vertical axis is the transformation start temperature of the acicular ferrite; FIG. 4B shows the relationship between the driving force and the time of the non-diffusion transformation that can be obtained by thermodynamic calculation. Each shows. For convenience of explanation, FIG. 4 also includes a graph 4c for determining the transformation calculation end temperature of acicular ferrite, but the explanation of FIG. 4c will be described later.

  First, as shown in FIG. 4B, the driving force of the non-diffusion transformation becomes larger than 400 to 800 J / mol (Df in the figure) when the temperature is lowered (continuous cooling) as time passes. In the present invention, the temperature at which the driving force of the non-diffusion transformation reaches Df (400 to 800 J / mol) [(i) in FIG. 4 (a)] is the transformation start temperature of acicular ferrite (calculation start temperature). ).

(B-2) Calculation of acicular ferrite transformation rate X _AF (T) when held at temperature T and determination of transformation calculation end temperature Next, the transformation calculation start temperature is determined by the method of (b-1) above. (B-2) Calculate the transformation rate of acicular ferrite from the above transformation calculation start temperature, determine the transformation calculation end temperature of acicular ferrite, and calculate up to the transformation calculation end temperature. values, and acicular ferrite transformation ratio X _AF of the weld metal portion.

  Hereinafter, it will be described in detail including a basic experiment that has reached the above calculation method.

  In order to calculate the acicular ferrite transformation rate of the weld metal part, the present inventors first, based on the viewpoint that it is necessary to determine the nucleation and growth status of the acicular ferrite and the form of the acicular ferrite, The specimen of the weld metal part was subjected to the heat treatment simulator shown in FIG. This figure was originally constructed by the present inventors as a heat treatment pattern capable of generating as much acicular ferrite as possible in a weld metal part.

  The heat treatment will be described with reference to the same drawing. First, the specimen is heated to an Ac3 point or higher to be held, thereby forming an austenite single phase. In order to obtain the desired acicular ferrite, it is necessary to generate a large amount of larger austenite in advance. For this purpose, it is recommended to keep the heating temperature as high as possible for a long time. Next, after rapidly cooling to a temperature range of 500 to 620 ° C. (25 ° C./s or more), holding at that temperature for a predetermined time (isothermal holding) and then water cooling, it was found that desired acicular ferrite was obtained. In the present invention, the holding time in the isothermal holding is variously changed, and this makes it possible for the first time to grasp the nucleation / growth process of acicular ferrite, which could not be grasped conventionally.

  Incidentally, it can be considered that the reason why the acicular ferrite transformation rate during the isothermal transformation could not be calculated conventionally is that the above-mentioned holding temperature (500 to 620 ° C.) was not appropriate. When the holding temperature is below 500 ° C, the transformation of acicular ferrite is very fast (it immediately forms and immediately disappears), so the nucleation / growth process of acicular ferrite cannot be captured, while the holding temperature is It has been clarified for the first time by experiments of the present inventors that when the temperature exceeds 620 ° C., the temperature becomes too high and the desired acicular ferrite is not generated.

  As a result of the basic experiment based on the heat treatment, the nucleation rate of the acicular ferrite is very fast as shown in FIG. 5, and it is set as site saturation (a situation where all the nucleation sites are consumed immediately after the transformation starts). A detailed analysis of the growth process assuming that the shape of the acicular ferrite is plate-like (length L, width W) shows that the growth is instantaneously completed immediately after transformation in the length (L) direction. After that, it became clear that diffusion growth occurred in the width (W) direction.

In the “prior invention”, based on such knowledge, the acicular ferrite transformation rate X _AF (T) when held at the temperature T is calculated as a crystallization of the weld metal part by the step (a). It is specified by a function A ₀ (N, T) of information N and temperature T.

On the other hand, in the present invention, factors relating to the form of acicular ferrite (side area A, plate thickness W, and density) can be easily calculated as an acicular ferrite transformation rate X _AF (T) at temperature T. The following formula (1) represented by P) is specified. Therefore, in the method of the present invention, it is not necessary to create a database of A ₀ (N, T) as in the “prior invention”.
X _AF (T) = 1−exp (−A _T × P _T × W _T ) (1)
_Where X _AF (T) is the AF transformation rate at temperature T;
A _T is the AF side area at temperature T (m ² );
P _T is the density of AF at temperature T (pieces / m ³ );
W _T is the plate thickness (m) of AF at temperature T;
W _T = α × t ^1/2 ,
α is assumed when AF is transformed in para-equilibrium.
Parabolic rate constant;
t is the holding time at temperature T (seconds)
Means
The (A _T × P _T ) is represented by the following formula (2).
(A _T × P _T ) = − 1.699 × 10 ⁵ −7.506 × 10 ² × (dGγ → α)
(2)
Where (dGγ → α) is from austenite to ferrite at temperature T
Driving force of non-diffusion transformation when transforming to (J / mol)
It is.

  Hereinafter, the requirements [each parameter and formula (2)] constituting the above formula (1) will be described.

(I) A _T : AF side area at temperature T (m ² )
The acicular ferrite that is a prediction target of the present invention is a “plate-like acicular ferrite” having a side area A and a plate thickness W as shown in FIG. As described above, the growth process of such a plate-like acicular ferrite is completed immediately after nucleation in the length direction (corresponding to the longitudinal direction L and the side area A). The side area _AT is considered constant regardless of time.

(Ii) P _T : AF density at temperature T (pieces / m ³ )
The density P _T of AF at the temperature T, per unit volume (m ^3), the number (the invention of the plate-shaped acicular ferrite [lateral area A (≒ length L), the thickness (width) W], Since it is assumed that the nucleation behavior of the acicular ferrite is site saturation, this means that the number of nucleation sites is the same as the number of nucleation sites).

(Iii) Formula (2) In calculating X _AF (T) represented by the above formula (1) in the present invention, the product of the side area A _T and the density P _T represented by the following formula (2) ( A _T × P _T ) may be used. As shown in the formula (2), (A _T × P _T ) is a non-diffusion transformation driving force when transforming from austenite to ferrite “dGγ → α” (J / mol; hereinafter may be represented by Df) Expressed as a function of
(A _T × P _T ) = − 1.699 × 10 ⁵ −7.506 × 10 ² × (dGγ → α)
(2)
Here, the process of determining the above formula (2) will be described.

First, using a base material of JIS SM490, in the wire component (YGW-11) of JIS standard, C, Si, and Mn, which are the main components, were respectively changed as shown in Table 1 below (No. 1-6), for each wire sample, the holding temperature (holding temperature in the heat treatment simulator shown in FIG. 2) is changed to three levels of 550 ° C., 570 ° C., and 600 ° C., and others As shown in Table 2 below, welding was performed, and the acicular ferrite area ratio formed when welding was performed under a total of 18 conditions (6 components × 3 levels) was first determined. That is, in the micrograph as shown in FIG. 6, one field of view of 2400 μm ² is observed in three fields of view to determine the area ratio of the acicular ferrite (in FIG. 6, the white elongated one is the acicular ferrite), and then The acicular ferrite transformation rate was calculated from (area ratio of the acicular ferrite) / (ferrite phase fraction in the equilibrium state determined by thermodynamic calculation).

By the way, in the AF transformation model formula (plate-like) represented by the following formula (4), if A ₀ N = A × P is modified as in the following formula (5), A × P under each condition becomes Α can be determined by thermodynamic calculation at the holding temperature, and the acicular ferrite transformation rate X (t) at time t can be determined as described above.

  Then, the above formula (2) is specified by inputting the obtained A × P value, the basic data of the weld metal composition and holding temperature into commercially available thermodynamics (Thermo-Calc (Foundation for Computational Thermodynamics)) I was able to do it.

(Iv) W _T : AF plate thickness at temperature T (m ² )
Thickness W _T of AF at the temperature T is expressed by W _T = α × t ^1/2. As described above, in the growth process of the plate-like acicular ferrite, the growth is instantaneously completed immediately after nucleation in the length direction (corresponding to the longitudinal direction L and the side area A), and thereafter, the width (plate This corresponds to diffusion growth in the direction corresponding to the thickness W).

  Here, “α” means a state in which the acicular ferrite is transformed into a para-equilibrium [the substitutional solid solution element such as Si and Mn does not have time to diffuse, specifically, the substitutional solid solution element. Is the parabolic rate constant when it is assumed that the austenite and ferrite are in the same (equilibrium) state]. In calculating the above W, the reason for adopting a constant when the acicular ferrite is transformed by para-equilibrium, such as `` α '', is that the acicular ferrite is produced by the transformation of austenite to ferrite, This is because the acicular ferrite is considered to be most easily generated when transformed by para-equilibrium.

  The above α can be calculated based on the composition and temperature of the weld metal part on the assumption that acicular ferrite is transformed by para-equilibrium. Specifically, α may be calculated using a program described in CAMP-ISIG, Vol. 3 (1990), p871, or another commercially available program [Thermo-Calc (Foundation for Computational Thermodynamics)]. In the examples described later, α was calculated using the former program.

  On the other hand, since the actual measured value of the plate thickness W cannot be actually measured, the short axis length is compared with the short axis length when the acicular ferrite is observed two-dimensionally instead of one-dimensionally. The AF side area W (measured value) was estimated. This is because it is known that the plate thickness W and the minor axis length have a correlation.

The equation (1) for deriving the acicular ferrite transformation rate X _AF (T) when held at the temperature T has been described above.

Next, starting from the transformation calculation start temperature of the acicular ferrite determined by the method (b-1), the acicular ferrite transformation rate X _AF (T) at the temperature T is calculated by the method described above. Finally, a method for calculating the acicular ferrite transformation rate of the weld metal part will be described.

As described above, X _AF (T) is only the acicular ferrite transformation rate when held at temperature T, and is formed when the temperature continuously changes (continuous cooling) in actual welding. It is not the “acicular ferrite transformation rate of the weld metal”.

Therefore, in the present invention, in calculating the “acicular ferrite transformation rate of the weld metal part”, the cooling temperature history of (a) is divided into minute times (Δt), and the temperature T at each minute time (Δt) is calculated. By sequentially calculating the acicular ferrite transformation rate X _AF (T), the acicular ferrite transformation rate of the weld metal part at the end of the final welding pass was predicted. This is because, during the minute time Δt at the temperature T, X _AF (T) is obtained on the assumption that the isothermal transformation proceeds at the temperature T, and this is repeatedly added (addition rule). This is to predict the “acicular ferrite transformation rate of the weld metal part” after welding (see FIG. 7). Such a method is not limited to the present invention, and is generally used in the “property prediction method”. It is generally practiced.

The calculation of X _AF (T) described above is performed up to the temperature at which transformation of the acicular ferrite ends (transformation calculation end temperature). Hereinafter, a method for determining the transformation calculation end temperature of the acicular ferrite will be described.

  The transformation calculation end temperature of the acicular ferrite is determined based on the composition of the weld metal part and the cooling temperature history. Specifically, (1) the carbon amount Cγ in the untransformed austenite and the carbon amount at the Acm point. The temperature at which C (Acm) intersects; or (2) When T0 is the higher temperature among the Ms points, the temperature is in the range of T0 to (T0-50 ° C).

  Hereinafter, a method for determining the transformation end temperature of acicular ferrite will be described in detail with reference to FIG. FIG. 4C shows the temporal transition of the carbon content Cγ in untransformed austenite and the carbon content C (Acm) at the Acm point (critical point where cementite is formed). For convenience of explanation, FIG. 4 also includes graphs (a) and (b) for determining the transformation calculation start temperature of acicular ferrite, but these explanations are as described above. is there.

  As described above, when the temperature decreases with time (continuous cooling), the non-diffusion transformation driving force (dGγ → α) is 400 to 800 J / mol (in the figure) as shown in FIG. In the present invention, the temperature at which the driving force of the non-diffusion transformation reaches 400 to 800 J / mol [(i) in FIG. 4 (a)] is the transformation of the acicular ferrite. It is defined as the start temperature (calculation start temperature).

  As the temperature further decreases, the acicular ferrite transformation proceeds, so that the carbon content Cγ in the untransformed austenite increases as shown in FIG. 4 (c). On the other hand, the carbon content C (Acm) at the Acm point decreases as the temperature decreases. The temperature when the carbon content Cγ in the untransformed austenite and the carbon content C (Acm) at the Acm point intersect is (iii) in FIG. 4 (a). This is because all the untransformed austenite has undergone pearlite transformation. (That is, the temperature at which the acicular ferrite transformation ends).

  On the other hand, the temperature Ms point [(ii) in FIG. 4 (a)] generated by martensite can be obtained by thermodynamic calculation.

  Of the calculated (iii) in FIG. 4 (a) [temperature at which carbon amount Cγ in untransformed austenite and carbon amount C (Acm) at Acm point intersect], and Ms point in (ii) When the higher temperature is T0, the range from T0 to (T0-50 ° C.) is defined as the transformation end temperature of acicular ferrite. It has been confirmed by experiments that the acicular ferrite transformation rate can be accurately predicted within this temperature range.

  Incidentally, in FIG. 4 above, since the temperature of (iii) is higher than the temperature of (ii), the reference temperature T0 of the acicular ferrite transformation end temperature is (iii), from the temperature of (iii) to a temperature range lower by 50 ° C. Is the transformation calculation end temperature of the acicular ferrite in the present invention.

When the transformation end temperature of the acicular ferrite is determined in this manner, the calculation of the acicular ferrite transformation rate X _AF (T) at the temperature T is also finished. The cure ferrite transformation rate is calculated.

  The acicular ferrite transformation rate prediction means for the weld metal part has been described based on the above (b-1) to (b-2).

Furthermore, the present invention includes a method for predicting the characteristics of a weld metal part, which is characterized by predicting the mechanical characteristics of the weld metal part based on the above prediction method. Specifically, the relationship between the acicular ferrite transformation rate of the weld metal part formed by a single pass or multiple passes and the mechanical properties of the weld metal part is determined in advance,
By collating the acicular ferrite transformation rate of the weld metal part calculated by any of the prediction methods described above, and the relationship between the predetermined acicular ferrite area ratio of the weld metal part and the mechanical properties, This is a method for predicting the mechanical properties of the weld metal part.

  This is because a database on the relationship between the acicular ferrite transformation rate and the mechanical properties is created in advance, and the acicular ferrite transformation rate calculated by the prediction method of the present invention is collated with the results of the above database. The mechanical characteristics of the weld metal part can be predicted accurately and easily based on the acicular ferrite transformation rate.

(2) About the method for predicting the shape of the acicular ferrite in the weld metal part Next, the method for predicting the form of the acicular ferrite in the weld metal part according to the present invention will be described in detail with reference to the drawings. FIG. 8 is a flowchart showing a procedure for carrying out the method of the present invention, which is created assuming a welding operation represented by arc welding by using a base material and a welding material and using a single pass or a plurality of passes. is there. Specifically, it is implemented using a material prediction computer in which a program for executing each means is stored in a storage device.

Here, the form prediction method is
(A) Basic information calculation means for calculating the composition of the weld metal part, the crystallized substance information, and the cooling temperature history from the first welding pass to the final welding pass based on the respective components of the base material and the welding material and the welding conditions. When,
(C) includes a method for predicting the shape of the acicular ferrite of the weld metal portion, which is calculated based on the basic information calculation means of (a), and predicts the shape of the acicular ferrite at the end of the final welding pass,
The shape of the acicular ferrite (AF) is represented by the product of the side area A (m ² ) and the plate thickness W (m),
In (c), the cooling temperature history in (a) is divided into minute times, and the AF side area A _T and (A _T × P _T ) at the temperature T in each minute time (where P _T is , Which is the density of AF at temperature T), the AF side area A (m ² ) of the weld metal portion at the end of the final welding pass, the plate thickness W (m) of the AF, and the AF Density P (pieces / m ³ ), respectively,
The _AT is calculated based on the following formula (3):
The (A _T × P _T ) is calculated based on the above equation (2).
A _T = β × P _T ^-2/3 (3)
Where A _T is the AF side area at temperature T (m ² );
β is a proportionality constant;
P _T is the density of AF at temperature T (pieces / m ³ )
It is.

  Among them, the basic information calculating means (a) is the same as (a) described in the method for predicting the acicular ferrite transformation rate (1) described above, and the description thereof is omitted.

  Next, the “acicular ferrite form prediction means of the weld metal part” of (c) will be described.

(C) Acicular ferrite shape prediction means of weld metal part The above (c) is based on the transformation start temperature and transformation end temperature of the acicular ferrite calculated by thermodynamic calculation. The side area A (m ² ) of the acicular ferrite, the plate thickness W (m) of the acicular ferrite, and the density P (pieces / m ³ ) of the acicular ferrite are predicted, respectively. It is expressed as “acicular ferrite shape prediction means of weld metal part”.

Specifically, in carrying out the above (c), first, (c-1) the temperature at which the acicular ferrite starts transformation (transformation calculation start temperature) is determined, and (c-2) the transformation calculation is started. The shape of the acicular ferrite is calculated from the temperature [specifically, the side area A _{T of} the acicular ferrite at the temperature T at each minute time when the cooling temperature history is divided into minute times, and ( A _T × P _T ) (where P _T is the density of AF at temperature T) is calculated sequentially, and the carbon concentration Cγ in the untransformed γ corresponding to the transformation rate of the acicular ferrite The temperature when Cγ satisfies the transformation end condition (described later) is defined as the temperature at which the acicular ferrite finishes transformation (transformation calculation end temperature), and the calculated values up to the transformation calculation end temperature are respectively determined. ,welding The side area A, the plate thickness W, and the density P of the acicular ferrite of the metal part are set.

  Hereinafter, the above (c) will be described in detail with the background of the basic experiment.

(C-1) Determination of transformation calculation start temperature of acicular ferrite This step is the same as (b-1) described above, and a description thereof is omitted.

(C-2) Calculation of side area A _T and (A _T × P _T ) of acicular ferrite when held at temperature T and determination of transformation calculation end temperature Next, the method of (c-1) above After determining the transformation calculation start temperature by (c-2), the side area A _T and (A _T × P _T ) of the acicular ferrite is calculated from the above transformation calculation start temperature, and the acicular is calculated. The transformation end temperature of ferrite is determined, and the side area A (m ² ), the thickness W (m), and the density (pieces / piece) of the acicular ferrite of the weld metal part based on the calculated values up to the end temperature of the transformation calculation. m ³ ) is determined respectively.

Hereinafter, it will be described in detail including a basic experiment that has reached the above calculation method.
First, how the following equation (3) is derived will be described.
A _T = β × P _T ^-2/3 (3)
Where A _T is the AF side area at temperature T (m ² );
β is a proportionality constant;
P _T is the density of AF at temperature T (pieces / m ³ )
It is.

In the determination of the above formula (3), as a premise, the length when the plate-like acicular ferrite (the major axis length is L and the minor axis length is W) is generated from the nucleation site and grown ( The length in terms of how far the major axis and the minor axis grow) is defined as the length when the acicular ferrite collides with another acicular ferrite. This is because the growth of the acicular ferrite is considered to stop when the two acicular ferrites collide. Under such preconditions, it is considered that the major axis and minor axis of acicular ferrite are both proportional to the average distance of the nucleation site, “Metromorphology (Uchida Otsukuru) 1972” (Kunio Makishima) , Shinohara Yasutada, Komori Naoshi) can be used.
Average distance of point-like particles (nucleation sites) ∞ N ^-1/3
On the other hand, the side area A of acicular ferrite is A = L ²
Therefore, A is finally specified by the above formula (3) when the proportionality constant is β.

In the above equation (3) derived in this way, (A _T × P _T ) can be determined by the equation (2) used in the above-mentioned “means for predicting transformation rate of acicular ferrite”. If it is known, the AF side area A, the plate thickness W, and the density P of the weld metal part can be obtained by calculation.

  Here, there are the following three methods for calculating β.

  In the first calculation method, after actually producing a weld metal part using a wire and a base material, the measured values of A and P constituting the above equation (3) are calculated, and the value of β (experimental value) is calculated. It is a method of determination. Among these, the measured value of A and P can adopt the method obtained when dGγ → α is derived.

  The second calculation method is a method that uses existing experimental values, and specifically, β when welding is performed under conditions that approximate the actual welding conditions (conditions in which the component system and the holding temperature are substantially the same). (Experimental value) may be applied. This calculation method is a very simple method in that it is not necessary to calculate an experimental value every time welding is performed as in the first calculation method. β is a geometrically determined constant and, unlike the above-described dGγ → α, it has been confirmed by the basic experiments of the present inventors that it is hardly influenced by the composition and holding temperature of the weld metal.

  The third calculation method is a method of calculating the value of β (calculated value, β = 1 to 3) based on the basic experiment described below. It has been confirmed by experiments that the shape of acicular ferrite can be predicted with high accuracy even if this calculated value is used.

The details of the basic experiment are as follows. First, using a base material of JIS SM490, in the wire component (YGW-11) of JIS standard, C, Si, and Mn as main components were respectively changed as shown in Table 1 above (total No. 6 components). 1) to 6), and for each wire sample, the holding temperature was changed to three levels of 550 ° C., 570 ° C., and 600 ° C., and the other conditions were as shown in Table 2 above. And A _T × P _T under a total of 18 conditions (6 components × 3 levels) is obtained by the same method as described above. Further, P _T is obtained by measuring the density per unit area using a scanning electron microscope and converting it to the density per unit volume. Then, A _T × P _T and P _T obtained in this way are introduced into the following equations (6) and (7) to obtain β.
A _T × P _T = X1 (6)
A _T = β × P _T ^−2/3 (7)
[X1 and P _T in Equations (6) and (7) are experimentally determined values]

  When an average value of β under a total of 18 conditions is obtained, β = 1 to 3 is obtained. Experiments have confirmed that the shape of acicular ferrite can be accurately predicted if β is within the above range. β is preferably 1.5 or more and 2.5 or less. In the examples described later, this third calculation method was adopted.

  After β is determined by any of the methods described above, the side area A and the density N of the acicular ferrite can be obtained by calculation based on the above equations (3) and (2), respectively.

  Further, the plate thickness W of the acicular ferrite can be calculated by the above formula (1) and the above formula (3).

The equation (3) for deriving the side area A _T , the plate thickness W _T , and the density P _T of the acicular ferrite when held at the temperature T has been described above.

Next, starting from the transformation start temperature of the acicular ferrite determined by the above method (c-1), the side area A _{T of} the acicular ferrite at the temperature T, the plate thickness W _T , and The density _PT is calculated, and finally the form of the acicular ferrite of the weld metal part is calculated. This method is the same as the “addition rule” described in detail in “(1) Method for Predicting Transformation Rate of Acicular Ferrite” described above, and the method for determining the transformation calculation end temperature of acicular ferrite is also described in (1). Is the same.

  In the above, the acicular ferrite form prediction means of a weld metal part was demonstrated based on said (c-1)-(c-2).

  Furthermore, the above-described form predicting means of the present invention can be used as a method capable of accurately predicting the mechanical characteristics of the weld metal part. Specifically, this model may be incorporated in S14 “transformation structure calculation” of the flowchart shown in FIG. 1 of Patent Document 4 described above to obtain structure information of acicular ferrite.

  Hereinafter, the working effects of the present invention will be described more specifically by way of examples. However, the following examples are not of a nature that limits the present invention, and any design changes may be made in accordance with the gist of the present invention. It is included in the technical scope of

  In the following examples, if the acicular ferrite transformation rate prediction method and the acicular ferrite morphology prediction method of the present invention are used, even if raw materials having different components are welded under welding conditions having different heat input and cooling rates, the weld metal It is proved that the acicular ferrite transformation rate and the shape of acicular ferrite can be accurately predicted.

  Hereinafter, a method for calculating the predicted value and the actual measurement value for the acicular ferrite transformation rate of the weld metal part and the form of the acicular ferrite according to the experimental procedure will be described. In Table 7 to be described later, No. 1 performed in this example is shown. Details of the experimental conditions of 1 to 12 are summarized and shown in Table 8 above. The characteristics of 1 to 12 (transformation rate, density, side area, and plate thickness of acicular ferrite) are collectively described.

  For example, in Table 7, No. 1 will be described. 1 is No. 1 shown in Table 3. A wire of A is used for welding with the welding conditions changed from A to C (Table 6 described later), and the composition of the weld metal part is as shown in A of Table 4. No. above. In calculating the predicted value of the acicular ferrite transformation rate of 1, calculation conditions A (calculation start temperature is 600 ° C.) detailed in Table 5 and calculation end temperature (as shown in Table 6, for each welding condition) The difference from the calculation end reference temperature T0 is set to −10 ° C.). In addition, the above No. In calculating the predicted value of the 1 acicular ferrite form, β = 2.09 was used.

(1) Production mass% of weld metal part C: 0.15%, Si: 0.37%, Mn: 1.43%, balance: base material satisfying iron and impurities (thick steel plate with a plate thickness of 25 mm) And No. 2 shown in Table 3. Using the wires A to D (remainder: iron and impurities), CO ₂ gas shielded arc welding was performed under the following welding conditions (the following welding conditions A to C in which the heat input was changed).

Groove V type (opening angle 45 °)
Gap 6mm
Welding speed 20cm / min
5 passes
Interpass temperature 100 ° C
Heat input Welding condition A 15kJ / cm
Welding condition B 20kJ / cm
Welding condition C 30 kJ / cm
Shielding gas: CO ₂ 100%, 25L (liter) / min
Current-voltage-welding speed: 330A-38V-25cpm

(2) Measurement of acicular ferrite transformation rate of weld metal part (actual value)
Next, the weld metal thus obtained is mirror-polished and then corroded with 3% nital.
The structure was observed with a scanning electron microscope (S-4000 field emission electron microscope: magnification 2000 times).

  Among these, the acicular ferrite area ratio of the weld metal part was measured from the micrograph as shown in FIG. 6 using image analysis software [Image-Pro PLUS (MEDIA CYBERNETICS)], and this measured value was measured by welding. The acicular ferrite transformation rate (measured value) of the metal part was determined.

(3) Calculation of composition of weld metal part and calculation of cooling temperature history Calculation of Patent Document 4 described above based on the above base material component, the wire component (No. AD) in Table 3, and the above welding conditions AC. According to the method, the composition of the weld metal part and the cooling temperature history (cooling rate after the last austenite transformation) were calculated, respectively. The composition of the weld metal part after the end of welding is as shown in Table 4. The “cooling rate after the last austenite transformation” is as follows for each of the welding conditions A to C described above [for the purpose of organizing the contents of each welding condition, it is described in (1) above. The amount of heat input is also shown].
Welding condition A: Cooling rate after the last austenite transformation 26.4 ° C./sec
Heat input 15kJ / cm
Welding condition B: Cooling rate after the last austenite transformation 14.8 ° C./sec
Heat input 20kJ / cm
Welding condition C: cooling rate after last austenite transformation 6.6 ° C./sec
Heat input 30kJ / cm

(4) Calculation (predicted value) of acicular ferrite transformation rate of weld metal part)
(4-1) Determination of transformation calculation start temperature of acicular ferrite The transformation calculation start temperature of acicular ferrite was determined according to the method described above. Table 5 shows the details of the calculation conditions A to G implemented in this example, and the driving force Df of the non-diffusion transformation and the calculation start temperature of the acicular ferrite are written for each calculation condition A to G. is doing. Of these, the calculation conditions A to D and G are all examples of the present invention in which the temperature when Df reaches the range of 400 to 800 J / mol is set as the calculation start temperature; The temperature that reached Df = 1000 J / mol beyond the above range, and the calculation condition F is a comparative example in which the temperature that reached Df = 200 J / mol below the above range was the calculation start temperature.

(4-2) Calculation of X _AF (T) The transformation rate X _AF (T) of the acicular ferrite at the temperature T is calculated based on the following formula (1) [including the following formula (2)].
X _AF (T) = 1−exp (−A _T × P _T × W _T ) (1)
In the formula, X _AF (T), A _T , P _T and W _T have the same meaning as before,
The (A _T × P _T ) is represented by the following formula (2).
(A _T × P _T ) = − 1.699 × 10 ⁵ −7.506 × 10 ² × (dGγ → α)
(2)
In the formula, (dGγ → α) has the same meaning as before.

  Among these, dGγ → α constituting the above equation (2) corresponds to the above-mentioned Df, and the details are as shown in Table 5.

This dGγ → α was substituted into the above equation (2), and the product (A _T × P _T ) of the side area A and the density P of the acicular ferrite at the temperature T was calculated.

α was calculated based on the above document [CAMP-ISIJ, Vol. 3 (1990) p871]. The plate thickness W _{T of the} acicular ferrite at the temperature _T is calculated from the above α.

Next, the calculated values of (A _T × P _T ) and W _T were substituted into the above equation (1) to determine the acicular ferrite transformation rate X _AF (T) (predicted value) at the temperature T. The holding time T is Δt for holding at constant temperature.

(4-3) Measurement of acicular ferrite transformation rate of weld metal part Determine the transformation calculation end temperature of acicular ferrite according to the method described above. Table 7 shows the transformation calculation end reference temperature T0 and the calculation end temperature.

Next, based on the acicular ferrite transformation rate X _AF (T) at the temperature T obtained by the above-described method, the weld metal part from the starting temperature of the acicular ferrite transformation to the finishing temperature of the transformation of the acicular ferrite is measured. The acicular ferrite transformation rate (predicted value) was calculated.

  These results are shown in Table 8. In Table 8, “error” is the difference obtained by subtracting the actual measurement value from the predicted value of the acicular ferrite area ratio of the weld metal part, and is an index representing the accuracy of the predicted value. In the present invention, for each welding material, when the error when welding under different welding conditions A to C is obtained, the prediction accuracy is good only when the error satisfies within ± 10% in any case. It was judged that there was, and was evaluated as “example of the present invention”.

  FIG. 9 is a graph showing the predicted value and the actual measurement value of the acicular ferrite transformation rate (fraction).

(5) Calculation of the form of acicular ferrite (side area A, plate thickness W, density P) of the weld metal part (actual measurement value)
The measured values of the side area A, the plate thickness W, and the density P of the acicular ferrite of the weld metal part were calculated by the method described above.

  These results are shown in Table 8.

(6) Calculation of the shape of acicular ferrite (side area A, plate thickness W, density P) of the weld metal part (predicted value)
(6-1) Determination of transformation calculation start temperature of acicular ferrite For the transformation calculation start temperature of acicular ferrite, the result of (4-1) is used.

(6-2) Calculation of form of acicular ferrite at temperature T The form of acicular ferrite at temperature T is determined based on the following equation (3).
A _T = β × P _T ^-2/3 (3)
Where A _T , β, and P _T have the same meaning as before,
(A _T × P _T ) is calculated based on the following equation (2).
(A _T × P _T ) = − 1.699 × 10 ⁵ −7.506 × 10 ² × (dGγ → α)
(2)
In the formula, (dGγ → α) has the same meaning as before.

  Here, as shown in Table 7, the value of β is 2.09 [within the range of the present invention (β = 1 to 3). 1-7, 10-12], and 0.5 (examples below the range of the present invention; No. 9) and 20 (examples exceeding the upper limit of the present invention; No. 8).

Further, dGγ → α obtained in the above (4-2) is substituted into the above equation (2), and the product (A _T × P _T ) of the side area A _T and the density P _T of the acicular ferrite at the temperature T is calculated. Calculated.

α was calculated based on the above document [CAMP-ISIJ, Vol. 3 (1990) p871]. The plate thickness W _{T of the} acicular ferrite at the temperature _T is calculated from the above α.

Next, the calculated values of (A _T × P _T ) and W _T are substituted into the above equation (1) to determine the side area A _T and the density P _T of the acicular ferrite at the temperature T, respectively.

(6-3) Measurement of the shape of the acicular ferrite in the weld metal part Based on the side area A _T and the density P _T of the acicular ferrite at the temperature T obtained as described above, the starting temperature of the acicular ferrite transformation calculation Each form (predicted value) of the acicular ferrite of the weld metal part from the use of the acicular ferrite calculation end reference temperature T0 described in Table 4 to the transformation end temperature of the acicular ferrite was calculated.

  These results are also shown in Table 8.

  In the present invention, the predicted values and measured values of each form (side area A, plate thickness W, and density P) obtained in this way satisfy the following criteria: “The form prediction accuracy is good” And was evaluated as “Example of the Invention”.

Side area A of plate-like acicular ferrite: 75% ≦ (predicted value / measured value) ≦ 150%
Thickness W of plate-like acicular ferrite: 75% ≦ (predicted value / actual value) ≦ 150%
Density P of plate-shaped acicular ferrite: 75% ≦ (predicted value / measured value) ≦ 150%
9 to 11 are graphs showing the predicted value and the actual measurement value of the form of acicular ferrite (FIG. 10 shows the density, FIG. 11 shows the side area, and FIG. 12 shows the plate thickness).

  From the results in Table 8, it can be considered as follows.

  First, no. 1 to 4 and 10 to 12 are examples of the present invention implemented under conditions that satisfy all the requirements of the present invention. Even if the welding conditions are changed to A to C, the acicular ferrite transformation rate of the weld metal part, and Each form could be predicted with high accuracy.

  In contrast, no. 5 to 9 have the following problems.

  Of these, No. Nos. 5 to 7 are comparative examples in which the measurement error of the acicular ferrite transformation rate is large even if welding is performed under any of the welding conditions A to C. For details, see “No. 5 is calculated under the calculation condition E shown in Table 5 [the driving force in the non-diffusion state is set to be larger than the range of the present invention (400 to 800 J / mol)], the transformation start temperature of the acicular ferrite is Example of lowering; No. 6 is an example in which the transformation start temperature of the acicular ferrite is increased due to the calculation condition F (the driving force in the non-diffusion state is set smaller than the range of the present invention); No. 7 is an example in which the transformation end temperature of acicular ferrite was calculated beyond the allowable range of the present invention [the range of calculation end reference temperature T0 to (T0-50 ° C.)], and thus the end temperature was lowered. is there.

  Thus, when calculating the acicular ferrite transformation rate of the weld metal part under conditions that do not satisfy the requirements of the present invention, the measurement error increases when welding under different conditions by changing the heat input, etc. It turns out that it is insufficient to apply to.

  On the other hand, no. 7 to 9 are comparative examples in which β is out of the range (1 to 3) of the present invention and each form is calculated. Even if welding is performed under any welding condition A to C, the accuracy of acicular ferrite form prediction is high. Remarkably reduced. For details, see “No. In No. 7, since the calculation end temperature was dGγ → α = 1000 J / mol, the value of A × P was larger than the appropriate value, and both A and P were larger than the actually measured values. No. 8 is an example in which β exceeds the range of the present invention, and the predicted value of the acicular ferrite density P is very small, 0.1% of the actual measurement value. No. No. 9 is an example in which β falls below the range of the present invention, and the predicted value of the acicular ferrite density P is much larger than the actually measured value.

It is a schematic diagram of the ferrite containing acicular ferrite. It is a heat treatment simulator used in the present invention. It is a flowchart which shows the procedure for implementing the acicular ferrite transformation rate prediction method of this invention. It is a graph which shows the method of determining the transformation start temperature and transformation end temperature of acicular ferrite. It is a schematic diagram which shows a mode that an acicular ferrite grows. It is a microscope picture of acicular ferrite. FIG. 6 is a schematic diagram showing a concept of calculating “acicular ferrite transformation rate of weld metal part” from “acicular ferrite transformation rate at temperature T”. It is a flowchart which shows the procedure for implementing the acicular ferrite form rate prediction method of this invention. It is a graph which shows the result of the predicted value and measured value of the acicular ferrite transformation rate (fraction) in an Example. It is a graph which shows the result of the predicted value of the density P of acicular ferrite, and the actual value in an Example. It is a graph which shows the result of the predicted value and measured value of the side area A of acicular ferrite in an Example. It is a graph which shows the result of the predicted value of the thickness W of acicular ferrite, and the actual value in an Example.

Explanation of symbols

1 Arotriomorphic Ferrite 2 Widmanstatten Ferrite 3 Acicular Ferrite 4 Pearlite 5 Microface

Claims (11)

A method for predicting the acicular ferrite transformation rate of a weld metal part formed by a single pass or multiple passes,
(A) Basic information calculation means for calculating the composition of the weld metal part, the crystallized substance information, and the cooling temperature history from the first welding pass to the final welding pass based on the respective components of the base material and the welding material and the welding conditions. When,
(B) Based on the transformation start temperature and transformation end temperature of the acicular ferrite calculated by thermodynamic calculation, predict the acicular ferrite transformation rate of the weld metal at the end of the final welding pass. Including rate prediction means,
(B) divides the cooling temperature history of (a) into minute times, and sequentially calculates the acicular ferrite transformation rate X _AF (T) at the temperature T for each minute time, thereby completing the final welding pass. Is to predict the acicular ferrite transformation rate of the weld metal part at the time,
The shape of the acicular ferrite (AF) is represented by the product of the side area A (m ² ) and the plate thickness W (m).
X _AF (T) is calculated based on the following formula (1): A method for predicting the acicular ferrite transformation rate.
X _AF (T) = 1−exp (−A _T × P _T × W _T ) (1)
_Where X _AF (T) is the AF transformation rate at temperature T;
A _T is the AF side area at temperature T (m ² );
P _T is the density of AF at temperature T (pieces / m ³ );
W _T is the plate thickness (m) of AF at temperature T;
W _T = α × t ^1/2 ,
α is assumed when AF is transformed in para-equilibrium.
Parabolic rate constant;
t is the holding time at temperature T (seconds)
Means
The (A _T × P _T ) is represented by the following formula (2).
(A _T × P _T ) = − 1.699 × 10 ⁵ −7.506 × 10 ² × (dGγ → α)
(2)
Where (dGγ → α) is from austenite to ferrite at temperature T
Driving force of non-diffusion transformation when transforming to (J / mol)
It is.   The temperature history at the time of cooling from the highest temperature in the last heating and cooling process in which heating is performed at a temperature higher than the temperature at which austenite transformation is completed in multi-pass welding is used as the cooling temperature history of (a). The prediction method described in 1.   The transformation start temperature of the acicular ferrite of (b) is calculated based on the composition of the weld metal part and the driving force (dGγ → α) of the non-diffusion transformation by thermodynamic calculation. The prediction method described in 1.   4. The prediction method according to claim 3, wherein the transformation start temperature of the acicular ferrite of (b) is a temperature at which the driving force (dGγ → α) of the non-diffusion transformation becomes 400 to 800 J / mol. . The transformation end temperature of the acicular ferrite of (b) is determined based on the composition of the weld metal part and the cooling temperature history,
Temperature at which carbon content Cγ in untransformed austenite and carbon content C (Acm) at Acm point intersect; or Ms point, where T0 is the higher temperature, T0 (T0-50 ° C) range The prediction method according to any one of claims 1 to 4. A method for predicting the shape of acicular ferrite in a weld metal part formed by a single pass or multiple passes,
(A) Basic information calculation means for calculating the composition of the weld metal part, the crystallized substance information, and the cooling temperature history from the first welding pass to the final welding pass based on the respective components of the base material and the welding material and the welding conditions. When,
(C) includes a method for predicting the shape of the acicular ferrite of the weld metal portion, which is calculated based on the basic information calculation means of (a), and predicts the shape of the acicular ferrite at the end of the final welding pass,
The shape of the acicular ferrite (AF) is represented by the product of the side area A (m ² ) and the plate thickness W (m),
In (c), the cooling temperature history in (a) is divided into minute times, and the AF side area A _T and (A _T × P _T ) at the temperature T in each minute time (where P _T is , Which is the density of AF at temperature T), the AF side area A (m ² ) of the weld metal portion at the end of the final welding pass, the plate thickness W (m) of the AF, and the AF Density P (pieces / m ³ ), respectively,
The _AT is calculated based on the following formula (3):
The (A _T × P _T ) is calculated based on the following formula (2), and is a method for predicting the shape of acicular ferrite.
A _T = β × P _T ^-2/3 (3)
Where A _T is the AF side area at temperature T (m ² );
β is a proportionality constant;
P _T is the density of AF at temperature T (pieces / m ³ )
It is.
(A _T × P _T ) = − 1.699 × 10 ⁵ −7.506 × 10 ² × (dGγ → α)
(2)
Where (dGγ → α) is from austenite to ferrite at temperature T
It is the driving force (J / mol) of the non-diffusion transformation when transforming.   The form prediction method according to claim 6, wherein β is 1 to 3.   The temperature history at the time of cooling from the highest temperature in the last heating / cooling process in which heating is performed at a temperature higher than the temperature at which austenite transformation is completed in multi-pass welding is used as the cooling temperature history of (a). Or the form prediction method of 7.   The transformation start temperature of the acicular ferrite of (c) is calculated based on the composition of the weld metal part and the driving force (dGγ → α) of the non-diffusion transformation by thermodynamic calculation. The form prediction method according to any one of the above.   10. The morphology prediction according to claim 9, wherein the transformation start temperature of the acicular ferrite of (c) is a temperature at which the driving force (dGγ → α) of the non-diffusion transformation becomes 400 to 800 J / mol. Method. The transformation end temperature of the acicular ferrite of (c) is determined based on the composition of the weld metal part and the cooling temperature history,
Temperature at which carbon content Cγ in untransformed austenite and carbon content C (Acm) at Acm point intersect; or Ms point, where T0 is the higher temperature, T0 (T0-50 ° C) range The form prediction method according to any one of claims 6 to 10.

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