JPS63162810A - Manufacture of non-heattreated hot forged product - Google Patents

Abstract

PURPOSE:To manufacture a non-heattreated hot forged product having superior tensile strength and toughness, by subjecting a steel material contg. specified percentages of C, Si, Mn, P, S, Al, V and Cr to heating, forging and cooling under specified conditions. CONSTITUTION:A steel material consisting of, by weight, 0.08-0.15% C, 0.10-0.60% Si, 0.50-2.0% Mn, <=0.020% P, 0.010-0.120% S, 0.005-0.050% Al, 0.05-0.20% V, one or more among 0.05-0.50% Cr, 0.05-0.30% Cu, 0.05-0.50% Ni, 0.005-0.05% Nb and 0.005-0.03% Ti and the balance Fe with inevitable impurities is heated to 1,100-1,300 deg.C, forged in the austenite single phase region and cooled at 10-100 deg.C/min cooling rate in the temp. range of the Ar3-Ar1 transformation point to obtain a non-heattreated hot forged product having superior characteristics such as about 60kgf/mm<2> tensile strength, >=about 38kgf/mm<2> yield point and >=about 8kgf.m/cm<2> impact value.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a tensile strength (hereinafter referred to as TS) of 60 kgf/ms.
The above method for producing non-thermal hot forged products, especially for producing forged products for machine structures, requires no heat treatment after forging, that is, the required material properties (TS: > 60 kgf/m) are maintained without heat treatment.
”, Yield point (hereinafter referred to as YP): >38kgf/ms”
, Impact value (hereinafter referred to as uEgo): > 8 kgf-
+*/cj ].

<Prior Art> Many hot forged products for construction machinery, automobiles, etc. are used after being given the necessary strength and toughness by normalizing or hardening and tempering after forging.

However, recently, for the purpose of energy saving and cost reduction, for example, as disclosed in Japanese Patent Application Laid-Open No. 167751/1983,
After hot forging, carbonitride-forming elements are added to mild steel, and fine carbonitrides are precipitated in the ferrite without heat treatment, resulting in a tensile strength of 80 kg f/w” or more. It's starting to happen.

However, although it has a tensile strength of 80 kg f/w'' or more, it lacks toughness, and there has been a desire for a material that does not have that much tensile strength but has excellent toughness.

<Problems to be Solved by the Invention> The present invention provides forged products with a tensile strength of 60 ktf/am or more and toughness by omitting the heat treatment process that was conventionally required in order to save energy and reduce costs. By using steel materials with a specific composition range and appropriate cooling after hot forging, the required part properties (TS: >60kgf/-12, YP
: >38kgf/ms”, uEz.
: > 8 kgf -IO/cj)
This was done in order to provide a method for manufacturing non-thermal hot forged products that can be obtained as hot forged.

<Means for Solving the Problems> As a result of extensive research into the manufacturing method of non-thermal hot forged products, the present inventors have found that by using steel materials with a specific composition range and appropriate cooling after hot forging, We learned that the required properties of forged products could be changed, and based on this knowledge, we came up with this invention.

In the present invention, c: o, os ~ 0.15% violet (hereinafter abbreviated as %), Si: 0. lO~0.60%, Mn:
0.50-2.0, P: 0.020% or less,
S: 0.010-0.120%, Al:
0.005-0.050%, v: 0.05-0.2
0%, and further contains Cr: 0.05-0.50
%, Cu: 0.05”0.30%, Ni
: 0.05-0.30%, Nb: 0.00
5-0.05%, Ti: 0.005-0.03%
Steel materials containing one or more of the following elements, with the balance consisting of Fe and unavoidable impurities, are classified as
After heating to 00℃, forging in austenite single phase region, after forging Ar, ~Ar, transformation point temperature range lO ~ 100℃/■
This is a method for manufacturing a non-thermal hot forged product in which the product is cooled at a rate of in.

Effect> When a hot forged product is manufactured by the method of the present invention, the steel material having the above composition is cooled under appropriate conditions after hot working, so that the carbon (nit)ide forming elements V, Nb, and Ti Precipitation hardening of generated carbon(nitride) and Mn.

By strengthening and stabilizing the austenite matrix with Mn+Cr, Cu, and Ni, it is possible to obtain the strength and toughness required for mechanical parts even if the conventional heat treatment is omitted.

Next, the reason for limiting the component range will be explained.

C is an element necessary to obtain the strength of forged products,
If it is less than 0.08%, the strength will be insufficient, and if it exceeds 0.15%, the hardness will increase and the toughness will be impaired, so C is 0.08%.
The range was 0.15%.

Si is used as a deoxidizer in steelmaking and as an element that provides strength.
Si is required to be 10% or more, but if it exceeds 0.60%, the toughness deteriorates, so the content of Si is set in the range of 0.1n to 0.60%.

Mn is an element necessary for improving strength and toughness,
By heating to 1,100 to 1,300°C, it is sufficiently dissolved in austenite to provide the necessary strength and toughness to the part. The effect is small below 0.50%.
If Mn exceeds 2.00%, the toughness deteriorates, so if Mn exceeds 0.00%, the toughness will deteriorate.
It was made into the range of 50-2.00%.

Since P is an element that deteriorates toughness, it was set to 0.02% or less.

S is an element that improves machinability after forging, and its effect is small below 0%. In addition, if it exceeds 0.12%, it will have a negative effect on hot workability, so S should be 0.01%.
The range was 0.12%.

Al is added as a deoxidizing agent, and if it is less than 0.005%, its effect will be small, and if it exceeds 0.050%, it will have a negative effect on machinability, so Al should be added from 0.005 to 0.05%.
The range was 0%.

■ is an element necessary for improving strength and toughness, and 0.
If it is less than 0.05%, no significant improvement in strength will be obtained;
If it exceeds %, the strength will become too high and the toughness will deteriorate, so ■ was set in the range of 0.05 to 0.20%.

C is an element that strengthens the matrix and improves toughness when added in combination with V. If it is less than 0.05%, its effect is small, and if it exceeds O,SO%, the economic benefit decreases. , Cr was in the range of 0.05 to 0.50%.

Cu and Ni are elements that strengthen the matrix and improve strength and toughness, and if they are less than 0.05%, they have no effect, and if they exceed 0.30%, the economic benefits decrease, so Cu, The old range was 0.05% to 0.30%.

Nb is an element that forms carbon(nitride) and improves strength and toughness through precipitation hardening. '0
Nb is 0.005 to 0.05% because the effect is small below 0.05%, and the toughness deteriorates when it exceeds 0.05%.
The range of

Ti is an element that improves strength by converting carbon(nit)ride into +)i'', but if it is less than 0.005%, this effect is small, and if it exceeds 0.0396%, it may actually deteriorate the toughness. Therefore, Ti is 0.005-0.03%
The range of

Next, the heating temperature needs to be 1100°C or higher in order to fully dissolve V, Nb, and Ti in solid solution and to perform efficient forging. Therefore, the temperature was set at 1100 to 1300°C.

In addition, in order to obtain fine precipitates of carbon(nit)ride that cause precipitation hardening after hot working, it is necessary to set the cooling rate in the ~Ar+ transformation point temperature range to 10°C/man or more.
If the temperature exceeds 100℃/sin, there will be less carbon(nit)ride precipitates, resulting in insufficient strength.
And so. Note that the cooling rate may be adjusted by allowing the product to cool on a conveyor or the like after hot forging.

<Example> Using a material (billet) having the composition shown in Table 1, it was hot rolled into a round bar on a normal steel bar rolling line. There are two types of finished rolling dimensions: 313 mmφ and 85 mmφ, and this distinction is specified in the remarks column of Table 1. The material steels up to sample NaA-L are steels within the composition range of the present invention, and sample NIM
The material steel is a comparative material.

The material steel of 33m φ is 2011φ after being heated to 1200℃.
The shaft is hot-forged, and then heated with Ar and placed in a cooling rate adjusting device with blast cooling function until the transformation end temperature.
The cooling rate between s and Ar, the modified Li temperature, and below the Ar+transformation temperature was adjusted to the above-mentioned rate.

After heating the steel material with a diameter of 85 mm to 1250°C, a cylindrical flange with a height of 1001 cm (dimensions at 1/2 height part: outer diameter 75
1■, Hot forged to inner diameter 25 mm), Ar, ~ Art change u'/? The cooling rate below x degrees and the Art temperature was adjusted in the same manner as the above 33m5φ cable steel.

Next, JIS No. 4 tensile test pieces, JIS No. 3 impact test pieces, and hardness test pieces were taken from the shafts and flanges obtained in this way, and the material properties were investigated, and the results shown in Table 2 were obtained. . From Table 2, it can be seen that the products manufactured by the method of the present invention have strength, hardness, and toughness equivalent to or higher than those of the comparative 111M reheated products in the as-forged state. In addition, among the samples in the comparative example, the cooling rate in the transformation temperature range of Ar, ~A, and H composition was 3
It can be seen that in the case of 'c/sin, the strength and hardness are inferior because the carbon (nit)ride size becomes large.

Therefore, according to the method of the present invention, plate parts having a strength of 60 kgf/m", which were conventionally heat-treated after hot forging, can be provided as they are after hot forging.

<Effects of the Invention> According to the method of the present invention, the required component characteristics (TS: >60ktf/a) can be maintained even if the conventionally required heat treatment step is omitted.
m”, YP: >38kgf/am”
, uEgo: > 8 kgf −m
/cd) can be obtained,
We were able to save energy and reduce costs.

Claims (1)

[Claims] C: 0.08 to 0.15% by weight (hereinafter abbreviated as %), Si
:0.10~0.60%, Mn:0.50~2.0%,
P: 0.020% or less, S: 0.010-0.120%
, Al: 0.005 to 0.050%, V: 0.05 to 0.20%, and further Cr: 0
．． 05-0.50%, Cu: 0.05-0.30%, N
i: 0.05-0.30%, Nb: 0.005-0.0
5%, Ti: 0.005 to 0.03%, and the remainder is Fe and unavoidable impurities after heating the steel material to 1100 to 1300°C to form an austenite single phase region. After forging, Ar_3~Ar_
1. A method for producing a non-thermal hot forged product characterized by cooling the transformation temperature range at a rate of 10 to 100° C./min.