CN101412174A - Method for confirming preheating temperature of steel material welding - Google Patents

Abstract

The invention provides a method for determining the preheating temperature for welding a steel material, which mainly solves the problems that the prior method has long testing period and high detection cost. The method comprise the following process: according to a selected and tested steel material sample, welding parameters are set; according to different set welding speeds, n weld beads are fused and applied on the sample; a hardness test is carried out on a transverse cutting block of each weld bead; the welding speed of the former weld bead of a hardening tissue with certain fusing and applying speed is used as the welding speed of the maximal safety value for the cooling speed of the steel material; according to the welding speed of the maximal safety value for the cooling speed of the steel material, a formula of the critical cooling speed of the steel material is utilized to calculate the critical cooling speed of the sample; and according to the actually-used welding process parameters, a formula of the preheating temperature is utilized to calculate the preheating temperature of the steel material. The method has the advantages of simple testing, easy realization and the accurate determination of the preheating temperature, can effectively prevent the generation of welding cracks and can be used for determining the preheating temperature of the welding of various new steel materials and special steel materials.

Description

Method for confirming preheating temperature of steel material welding

Technical field

The inventive method relates to mechanical welding technology field, particularly relates to a kind of method for confirming preheating temperature of steel material welding.

Background technology

Welding processing is one of main method of present machining.In the welding processing process since the actual cooling velocity of weld metal greater than the critical cooling rate of steel, in weld seam and heat affected area, just may produce martensitic structure, when having hydrogen and welding stress, just may produce as crackle, be mingled with, weld defect such as pore and slag inclusion.For fear of generation of defects, generally adopt the control and the post weld heat treatment of weld preheating, welding process.At present, the method of determining preheating temperature of steel material welding mainly contains following two kinds: (1) searches different cooling conditions, prediction material structure and hardness according to the steel heat simulated test from the CCT figure of welding heat affected zone, thereby determine the material welding pre-heating temperature, the defective of this method is long, a detection cost height of test period.(2) preheat temperature of from relevant welding handbook, searching institute's welding material according to type of steels, the defective of this method is to satisfy the requirement of all material, because the welding handbook has only been enumerated the preheat temperature of common used material, can't find for new material and special material.Along with science and technology development, particularly high-strength steel and super-high strength steel application of novel material are more and more wider, thereby this method can not be suitable for the application of new material and special material.

Summary of the invention

Purpose of the present invention is to overcome the deficiency of above-mentioned prior art, provide a kind of test period short, detect the low method for confirming preheating temperature of steel material welding of cost, effectively to prevent the generation of new material and special material weld defect.

The technical thought that realizes the object of the invention is actual from factory, utilizes existing welding equipment of factory and hardness detecting instrument, determines the preheat temperature of steel material welding.Its concrete technical process is as follows:

(1) selected tested steel are made sample;

(2), on welding equipment, set weldingvoltage U, welding current I and different welding speed V according to steel sample thickness δ _i

(3) according to different welding speed V i deposited n bar welding bead on sample of setting, n 〉=5;

(4) with every horizontal stripping and slicing of welding bead, in these strippings and slicings, carry out hardness test, and with occurring the speed of welding that a certain deposition rate has the last welding bead of hardened structure in the hardness test process, as the speed of welding of the maximum safety value of steel cooling velocity

(5) according to the speed of welding of the maximum safety value of steel cooling velocity

, utilize steel critical cooling rate formula to calculate the critical cooling rate V of sample _Cold

(6) according to critical cooling rate V _Cold, according to the steel welding speed V of reality use _t, welding current I ' and weldingvoltage U ', utilize the preheat temperature formula to calculate the preheat temperature of steel

Above-mentioned method for confirming preheating temperature of steel material welding, wherein the critical cooling rate v of the described calculating sample of step (5) _ColdRelative thickness δ according to steel _xAdopt following different formula:

δ _X〉=0.75, the employing formula is V _Cold=2 π λ (T _C-T ₀) ²/ E

δ _X＜0.75, the employing formula is V _Cold=2 π λ υ c (δ/E) ²(T _C-T ₀) ³,

In the formula

The expression weld heat input; η is the thermal efficiency;

Speed of welding for the maximum safety value of steel cooling velocity; The welding current that I sets for test; The weldingvoltage that U sets for test; λ is a metallic thermal conductivity; T _CTemperature for close pearlite nose on the overcooling austenite isothermal transformation diagram; T ₀For being that initial temperature is a room temperature before the steel welderings; υ is a steel density; C is a solid metal specific heat.

Above-mentioned method for confirming preheating temperature of steel material welding, the wherein described welding pre-heating temperature that calculates steel of step (6)

, according to the relative thickness δ of steel _XAdopt following different formula:

δ _X〉=0.75, adopt formula to be

δ _X＜0.75, adopt formula to be

E=η U ' I '/Vt in the formula, the expression weld heat input; η is the thermal efficiency; Vt is the steel speed of welding of actual use; I ' is the welding current of actual use; U ' is the weldingvoltage of actual use; λ is a metallic thermal conductivity; T _CIt is the temperature of close pearlite nose on the overcooling austenite isothermal transformation diagram; υ is the steel density; C is a solid metal specific heat; V _ColdBe the steel critical cooling rates.

The present invention determines the speed of welding of the maximum safety value of steel cooling velocity owing to utilized the existing instrument and equipment of factory to test, thereby calculates the preheat temperature of steel, so the test period is short, the detection cost is low; Welding current, weldingvoltage and speed of welding during simultaneously owing to employing actual welding when calculating preheat temperature, thereby the preheat temperature of determining is accurate, can effectively prevent the generation of weld crack, improves welding quality; Because the present invention tests simply, be easy to realize in addition, can further improve production efficiency.

Description of drawings

Fig. 1 is a flow chart of the present invention;

Fig. 2 is a welding bead schematic diagram of the present invention;

Fig. 3 is a welding bead stripping and slicing schematic diagram of the present invention.

The specific embodiment

With reference to Fig. 1, concrete steps of the present invention are as follows:

Step 1, selected tested steel are made sample.

The selected tested steel material trade mark, manufacturing thickness is 6mm, length and width are respectively 200mm and 150mm sample, and specimen surface oxide layer and cleaning oil pollution is clean.

Step 2 is set weldingvoltage U, welding current I and different welding speed V i on welding equipment.

According to the sample of 6mm thickness, on welding equipment, set the welding condition of sample respectively: weldingvoltage U=25V, welding current I=300A and five different welding speed V _i, but be not limited to 5, i.e. first welding speed V ₁=6mm/s, second welding speed V ₂=7mm/s, the 3rd welding speed V ₃=8mm/s, the 4th welding speed V ₄=9mm/s, the 5th welding speed V ₅=10mm/s.

Step 3 is according to the different welding speed V of setting _iEach deposited welding bead on sample.

As shown in Figure 2, on sample according to the welding bead of the deposited respective numbers of speed of welding number that is provided with, promptly with first welding speed V ₁The deposited first welding bead a of=6mm/s is with second welding speed V ₂The deposited second welding bead b of=7mm/s is with the 3rd welding speed V ₃Deposited the 3rd welding bead c of=8mm/s is with the 4th welding speed V ₄Deposited the 4th welding bead d of=9mm/s is with the 5th welding speed V ₅Deposited the 5th welding bead e of=10mm/s.

Step 4 is determined the speed of welding of the maximum safety value of steel cooling velocity

At first, with every horizontal stripping and slicing of welding bead, form 5 seam cross-section a ', b ', c ', d ' and e ', as shown in Figure 3.

Secondly, utilize hardness tester to carry out hardness test respectively successively in these seam cross-section, if find a certain seam cross-section hardened structure appears, then with the speed of welding of the pairing speed of welding of the last seam cross-section of this seam cross-section as the maximum safety value of steel cooling velocity.For example, hardened structure has appearred in seam cross-section d ' in the hardness test process, at this moment the pairing welding speed V of last seam cross-section c ' of this cross section d ' ₃=8mm/s is exactly the speed of welding of the maximum safety value of steel cooling velocity.

Step 5 is calculated the critical cooling rate V of tested steel sample _Cold

Speed of welding according to the maximum safety value of steel cooling velocity

Utilize steel critical cooling rate formula to calculate the critical cooling rate V of sample _Cold, the critical cooling rate V of this sample _ColdComputing formula is according to the relative thickness δ of steel _XThere are following two kinds:

Work as δ _X〉=0.75 o'clock, the employing formula was V _Cold=2 π λ (T _C-T ₀) ²/ E 1.

Work as δ _X＜0.75 o'clock, the employing formula was V _Cold=2 π λ υ c (δ/E) ²(T _C-T ₀) ³2.

Wherein

Expression weld heat input J/mm; η is the thermal efficiency, and steel generally get 0.9; Speed of welding mm/s for the maximum safety value of steel cooling velocity; The welding current that I sets for test; The weldingvoltage that U sets for test; λ is a metallic thermal conductivity, and the general value of steel is 0.028J/mm.s. ℃; T _CBe the temperature of close pearlite nose on the overcooling austenite isothermal transformation diagram, T usually _C=550 ℃; T ₀For initial temperature before the steel weldering, get 25 ℃ of room temperatures usually; υ is a steel density, usually υ=0.0078g/mm ³C is a solid metal specific heat, c=0.5J/g. ℃ usually.

The weld heat input of this example:

$E=\mathrm{\ηUI}/V_i^{\′}=0.90\×300\×25/8=843.75(J/\mathrm{mm}).$

The steel relative thickness passes through formula ${\mathrm{\δ}}_x=\mathrm{\δ}\sqrt{\mathrm{vc}(\mathrm{Tc}-\mathrm{To})/E}$ Determine.

To the sample of present embodiment thickness δ=6mm, calculate the relative thickness of steel according to this formula

${\mathrm{\δ}}_X=\mathrm{\δ}\sqrt{\mathrm{vc}(\mathrm{Tc}-\mathrm{To})/E}=6\×\sqrt{0.0078\×0.5\×(550-25)/843.75}=0.24$

Because δ _X=0.24＜0.75 belongs to the thin plate specification, so the steel critical cooling rate of utilizing above-mentioned formula 2. to calculate

V _Cold=2 π λ υ c (δ/E) ²(T _C-T ₀) ³

＝2×3.14×0.028×0.0078×0.5×(6/843.75) ²×(550-25) ³

＝5.017(℃/s)

Behind the rounding, get V _Cold=5 ℃/s.

Step 6 calculates the preheat temperature that steel weld

(6a), according to steel critical cooling rate V _Cold, according to the steel welding speed V of reality use _t, welding current I ' and weldingvoltage U ', utilize the preheat temperature formula to calculate the preheat temperature of steel

This preheat temperature is according to the relative thickness δ of steel _XObtain by following two kinds of different formula, work as δ _X〉=0.75, adopt formula to be

Work as δ _X＜0.75, adopt formula to be

E=η U ' I '/Vt in the formula, expression weld heat input J/mm; η is the thermal efficiency, and steel generally get 0.9; Vt is the steel speed of welding of actual use, present embodiment Vt=7mm/s; I ' is the welding current of actual use, present embodiment I '=250A; U ' is the weldingvoltage of actual use, present embodiment U '=25V; λ is a metallic thermal conductivity, and the general value of steel is 0.028J/mm.s. ℃; T _CBe the temperature of close pearlite nose on the overcooling austenite isothermal transformation diagram, T usually _C=550 ℃;

Be initial temperature before the steel weldering, i.e. steel preheating temperature ℃; υ is a steel density, usually υ=0.0078g/mm3; C is a solid metal specific heat, c=0.5J/g. ℃ usually; V _ColdBe steel critical cooling rate, V _Cold=5 ℃/s.

The weld heat input of present embodiment:

E＝ηU′I′/Vt＝0.90×250×25/7＝803.57(J/mm)。

(6b), according to actual plate thickness δ=9mm, by formula 3., the preheat temperature of primary Calculation steel

$5=2\×3.14\×0.028\×{(550-T_0^{\′\′})}^2/803.57$

Find the solution:

(6c), according to actual plate thickness δ=9mm, utilize relative thickness to pass through formula ${\mathrm{\δ}}_X=\mathrm{\δ}\sqrt{\mathrm{vc}(\mathrm{Tc}-T_0^{\′\′})/E}$ Determine the relative thickness of actual steel:

${\mathrm{\δ}}_X=\mathrm{\δ}\sqrt{\mathrm{vc}(\mathrm{Tc}-T_0^{\′\′})/E}=6\×\sqrt{0.0078\×0.5\×(550-399)/(0.9\×250\×25/7)}=0.244$

Because δ _X=0.244＜0.75 belongs to the thin plate specification, should adopt formula 4. to calculate its preheat temperature.

(6d), according to the actual steel relative thickness that calculates, utilize formula 4. to calculate the final preheat temperature T ＇ of steel ₀That is:

$5=2\×3.14\×0.028\×0.0078\×0.5\×{(9/803.57)}^2\×{(550-T_0^{\′\′})}^3$

Find the solution:

Because with more than this steel preheating to 163 ℃ the time, the weld seam cooling velocity is not more than 5 ℃/s, thereby can not produce crisp sclerous tissues in weld seam and heat affected area, also can not crack.

More than be a preferred embodiment of the present invention, but be not limited to the concrete numerical value that sets in the middle of the example.Any modifications and changes that can under technical scheme of the present invention, carry out different numerical value per capita, but these all belong to protection scope of the present invention.

Claims (4)

1, a kind of method for confirming preheating temperature of steel material welding comprises the steps:

(1) selected tested steel are made sample;

(2), on welding equipment, set weldingvoltage U, electric current I and different welding speed V according to steel sample thickness δ _i

(3) according to different welding speed V i deposited n bar welding bead on sample of setting, n 〉=5;

(4) with every horizontal stripping and slicing of welding bead, in these strippings and slicings, carry out hardness test, and with occurring the speed of welding that a certain deposition rate has the last welding bead of hardened structure in the hardness test process, as the speed of welding of the maximum safety value of steel cooling velocity

(5) according to the speed of welding of the maximum safety value of steel cooling velocity

Utilize steel critical cooling rate formula to calculate the critical cooling rate V of sample _Cold

(6) according to critical cooling rate V _Cold, according to the steel welding speed V of reality use _t, welding current I ' and weldingvoltage U ', utilize the preheat temperature formula to calculate the preheat temperature of steel

2, method for confirming preheating temperature of steel material welding according to claim 1, wherein step

(5) the critical cooling rate V of described calculating sample _Cold, according to the relative thickness δ of steel _XAdopt following different formulas:

δ _X〉=0.75, the employing formula is V _Cold=2 π λ (T _C-T ₀) ²/ E

δ _X＜0.75, the employing formula is V _Cold=2 π λ υ c (δ/E) ²(T _C-T ₀) ³,

In the formula $E=\mathrm{\ηUI}/V_i^{\′},$ Expression weld heat input J/mm,

η: the thermal efficiency,

The speed of welding of the maximum safety value of steel cooling velocity,

I: the welding current that test is set,

U: the weldingvoltage that test is set,

λ: metallic thermal conductivity J/mm.s. ℃,

TC: the temperature of close pearlite nose on the overcooling austenite isothermal transformation diagram,

T ₀: be that initial temperature is a room temperature before the steel weldering,

υ: steel density g/mm3,

C: J/g. ℃ of solid metal specific heat.

3, method for confirming preheating temperature of steel material welding according to claim 1, the wherein preheat temperature of the described calculating steel of step (6)

Relative thickness δ according to steel _XAdopt following different formula:

δ _X〉=0.75, adopt formula to be

δ _X＜0.75, adopt formula to be

E=η U ' I '/Vt in the formula, expression weld heat input J/mm,

η: the thermal efficiency,

Vt: the actual steel speed of welding of using,

I ': the actual welding current that uses,

U ': the actual weldingvoltage that uses,

λ: metallic thermal conductivity,

T _C: the temperature of close pearlite nose on the overcooling austenite isothermal transformation diagram,

υ: steel density,

C: solid metal specific heat,

V _Cold: the steel critical cooling rate.

4, according to claim 2 or 3 described method for confirming preheating temperature of steel material welding, wherein the steel relative thickness passes through formula ${\mathrm{\δ}}_x=\mathrm{\δ}\sqrt{\mathrm{vc}(\mathrm{Tc}-\mathrm{To})/E}$ Determine.

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