JPS62214158A - Production of cr steel products with jominy hardening end hardness assured - Google Patents

Abstract

PURPOSE:To produce Cr steel products with which the Jominy hardening end hardness is assured with high accuracy by producing an ingot of steel which is specified in the compsn. consisting of C, Si, Mn, Cr, Al, N, and Fe at the content of C controlled in accordance with the specific formulas. CONSTITUTION:The assigned hardness Hrc at the distance 1.5mm from the hardening end in the Jominy end hardening test for the steel products consisting of 0.10-0.60wt% C, 0.1-0.5% Si, 0.6-0.9% Mn, 0.85-1.20% Cr, 0.01-0.07% Al, <=0.02% N, and the balance Fe and inevitable impurities is made Hrc(1.5). The upper and lower limits of the content of C are controlled to the highest values of A=[Hrc(1.5)-23.3]/100% or B=[Hrc(1.5)-31.6]/62.9% or C=[Hrc(1.5)-42.7]/35.0% in accordance with the upper and lower limits thereof. The steel adjusted to the content of C controlled in the above-mentioned manner is produced and the Cr steel products with which the Jominy hardening end hardness is assured are obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing Cr steel with guaranteed hardenability, and more specifically, Cr steel having a chemical composition within a predetermined range was tested in the Jominy single-end quenching test. , when a range of Jominy quenched end hardness at a distance of 1.5 mm from the quenched end is specified, the amount of C in the steel material is accurately estimated and the chemical composition is determined so that the steel has the specified hardness. The present invention relates to a method of manufacturing a Cr steel material having the following properties.

(Prior Art) In order to obtain a predetermined strength and toughness, long steel bars made of structural alloy steel are manufactured by being quenched in most cases. Therefore, hardenability is an important characteristic of long steel bars made of structural alloy steel, and various methods for estimating such hardenability have been proposed and are also in practical use industrially.

As a method for estimating such hardenability, the Jominy single end quenching test is most commonly used, and a method of estimating Jominy hardness from the type and amount of alloying elements is known. For example, in hardening a round bar, the ideal critical diameter D
A method of estimating the Jominy hardness curve based on a constant coefficient of 1 and the distance from the hardened end and the hardened end hardness is well known. According to this method, the quenching hardness HRC(1,5) at a distance of 1°5m from the quenching end is HRC(1,5) = 32.3 + 59.8G when the C content is 0.40% or less. (%), and if the amount of C exceeds 0.40%, HRC (
1,5) -74,47,26/C(%) (However, C(
%) indicates the amount of C in % by weight. ) is given by

However, as a result of the detailed and extensive research conducted by the present inventors on the relationship between the hardened end hardness and the amount of C for Cr steel, the accuracy of the hardened end hardness based on these formulas is very poor, and in particular, It was found that when the amount of C was 0.2% or less, the difference from the actually measured value was extremely large. Furthermore, since the relationship between hardness and C content changes depending on the chemical composition of the steel, the above equation can be used to estimate with high accuracy the C content that provides the required Jominy hardened end hardness. I can't.

(Object of the Invention) Therefore, the present inventors conducted extensive research on the hardened end hardness in the Jominy single end quenching test for Cr1b materials having chemical components within a predetermined range, and found that 1. When the Jominy hardness at a position of 5 m is specified, based on this, a method of estimating the required amount of C with extremely high accuracy so as to have the specified quenching hardness was discovered, and the present invention was achieved. It is something that

(Structure of the Invention) The method of manufacturing a Cr steel material with guaranteed Jominy hardened edge hardness according to the present invention includes, in weight%, C0.10-0.60%, Si0.1-0.5%, Mn 0.6-0. .9%, Cr 0.85-1.20%, A4 0.01-0.07%, N 0.02% or less, the balance being iron and unavoidable impurities. Specified HII at a distance of 1.5fi from the hardened end in the test
When the C hardness is HRC (1, 5), based on the upper and lower limits, the upper and lower limits of the C amount are defined as the maximum amount of or, and steel having such a C amount is produced. It is characterized by

First, the reason for specifying the chemical composition of steel in the present invention will be explained.

The method of the present invention is applied to Cr1jl,
Therefore, it is necessary to add at least 0.10% of C to ensure the required strength.

However, when added in excess of 0.60%, the toughness deteriorates after quenching and tempering.

At least 0.1% of Si is added as a deoxidizing agent, but if it exceeds 0.5%, it causes a decrease in toughness.

At least 0.6% of Mn is added to ensure steel strength and to deoxidize, but when added in excess of 0.9%, the hardenability of the steel becomes too good and the It becomes impossible to obtain the amount of C using the formula defined in the invention.

Cr has the effect of improving the hardenability of steel, and in order to effectively obtain this effect, it is necessary to add 0.85% or more. However, when adding more than 1.20%, temper softening resistance increases and toughness deteriorates.

Al has the effect of deoxidizing and refining crystal grains.

In order to effectively obtain such an effect, at least 0.01
It is necessary to add %. However, addition of an excessive amount exceeding 0.07% causes blooming cracks during rolling.

N is added to refine the crystal grains, but 0.02
Addition of more than 0% causes blooming cracks during rolling.

In the method of the present invention, the amount of C is defined by the hardness HRC (1,5) at a distance of 1.5 from the quenched end in the Jominy one-end quench test, or the largest amount of or.

That is, HRC (1, 5) is usually specified within a certain range, but by substituting the upper limit into equations (1), (2), and (3) above, the largest amount among them can be calculated. The upper limit of the amount of C is defined by , and by substituting the lower limit of HRC (1, 5) into the above equations (1), (2), and (3), the lower limit of the amount of C is defined by the largest amount of them. be done.

(Effect of the invention) According to the method of the invention, Crf having a predetermined chemical component
For i, if the Jominy quenched end hardness is specified, if cl is calculated based on the above formula, Cr steel having such a C content will have the quenched end hardness specified above, regardless of other alloying elements. Therefore, according to the method of the present invention, the required chemical composition can be designed immediately from the specified quenched end hardness.

(Examples) The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples in any way.

Example I In Cr case hardening steel, the amount of C in a steel material having an HRC (1,5) of 40 to 42 is determined.

First, H*c(1,
By substituting 42 as 5), A=0.18
7, B=0.165 and C amount -0.02 are obtained, and among these, the largest amount, that is, 0.187% is obtained as the upper limit of C amount. In addition, H
By substituting 40 as RC(1,5), A
=0.1'i7, B=0.134 and C amount -0,077
of which the largest amount, i.e. 0.167%, was C
Obtained as the lower limit of quantity.

Therefore, the following chemical components C0.17%, Si0.26%, Mn0.74%, Cr 1.10%, A7! 0.03%, N 0.0120%, and measured its Jominy hardness. As a result, the Jominy hardness at 1.5 degrees from the quenched end was 41.0. The Jominy hardness at 5 mm from the quenched end was 31.2, and the Ruchominy hardness at 7fi from the quenched end was 26.3, indicating that the specified Jominy hardness was present.

Example 2 In Cr strong steel, H+te(1,5) is 56 to 58
If specified, the range of C amount is determined as 0.388% to 0.437% in exactly the same manner as in Example 1.

Therefore, the following chemical components C0.41%, Si0.19%, Mn0.70%, Cr 1.05%, A7! 0.034%, N 0.0035%, and measured its Jominy hardness. As a result, the Jominy hardness was 57.5 at 1.5 degrees from the quenched end, and 57.5 at 7 degrees from the quenched end. The Jominy hardness is 54.3, the Jominy hardness at 15fl from the quenched end is 45.3, and the Jominy hardness at 201 fl from the quenched end is 37.9, indicating that it has the specified Jominy quenched end hardness.

Claims (1)

[Claims] (1) C0.10-0.60%, Si0.1-0.5%, Mn0.6-0.9%, Cr0.85-1.20%, Al0.01-0.07% by weight , N0.02% or less, the balance is iron and unavoidable impurities. Then, based on the upper and lower limits, the upper and lower limits of the amount of C are A={[H_R_C(1.5)-23.3]/100}
(%) or B={[H_R_C(1.5)-31.6]/62.9
}(%) or C={[H_R_C(1.5)-42.7]/35.0
} (%), each of which is specified by the largest amount, and a method for manufacturing a Cr steel material with guaranteed Jominy hardened edge hardness, characterized by producing steel having such a C amount.