JPS58167749A - Quick carburized steel - Google Patents

Abstract

PURPOSE:To provide quick carburized steel wherein contents of Si, P and S as impurity elements are respectively limitted within a specific range and carburization cost is reduced by the acceleration of a carburization speed and the shortening of a carburization heat treatment time resulting form the componential adjustment of various case hardening steels. CONSTITUTION:An objective quick carburized steel is obtained by respectively limiting contents of Si, P and S as impurity elements in various case hardening steels such that Si is 0.05-0.25wt%, P is 0.005-0.015wt% and S is 0.002- 0.015%. In this case, the addition amount of an alloying element such as C, Mn, Cr, Ni or Mo is determined in a commonsense range required in securing hardenability and matrix hardness corresponded to the mass of applied parts. For example, Mn is adjusted so as to always hold a S/Mn ratio to 3X10<-2> or less by the S amount contained in a steel material. In addition, quick carburization steel can be shortened by 30% or more in a carburization time in a stable state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rapid carburizing case-hardening steel in which the carburizing speed is improved by adjusting the components of various case-hardening steels, the carburizing heat treatment time is shortened, and the carburizing cost is reduced.

In recent years, as an energy-saving measure for carburizing heat treatment, case hardening steel with rapid carburizing properties (rapid carburizing steel) has been developed with the aim of increasing carburizing efficiency, increasing hardenability and deepening the range of effective hardness. Case-hardened steel has been developed.

For example, the rapid carburizing steel shown in the table below has been developed.
This is due to the adjustment pressure of alloying element concentration #(@6).However, when investigating the ease of carburization of the current rapid carburizing steel, it is found that
Its carburizing properties show considerable variation, and its reliability is poor.

On the other hand, methods for accelerating the penetration of carbon into steel by ordinary gas carburizing include a method of increasing the carburizing temperature to increase the diffusivity of C, and a method of increasing carburizability by adjusting the steel alloy components.

The present invention is considered to be a companion to the above-mentioned circumstances, and its purpose is to provide a rapid carburizing steel that can stably shorten the carburizing time by 301 or more by adjusting the steel alloy components and increasing the carburizability. It is to be.

First, the present inventor carburized 8NCM 23 steel using the normal gas carburizing method (935°C, dew point -1δ°C to -20°C) for various times, and investigated the carbon concentration distribution at that time, as shown in the table in Figure 1. I am saddened by the results shown.

As a result, the surface carbon concentration gradually shifted to the high base element concentration side with time, and carburization increased to 8. It was found that the progress was significantly suppressed by surface segregation of impurities such as P.

Therefore, the present inventor investigated 81, P among various case hardening steels.

As a result of conducting various experiments in order to reduce the strong interfacial reaction resistance during carburizing by strictly regulating the concentration of impurity elements such as 8, and to improve the immersion properties and reliability thereof, the results of 81, P, 8. By regulating the concentration within the following range, we were able to improve carburizing properties and reliability.

sl α05~α25 wt%P α00
5~α015 #8 α002~α015 p+s α00f~α030 The addition amount of alloying elements such as CeMn, Cr + Ni a Mo, etc. should be adjusted to ensure hardenability and base hardness commensurate with the mass of the applied parts. Although it is determined within a necessary common sense range, Mn shall be adjusted so that the 8/Mn ratio is always 3 X I Cr2 or less depending on the amount of s contained in the steel material.

In addition, At + 11b* to prevent coarsening of crystal grains
The amounts of V and 'ri added are the same as in conventional carburized steel.

Next, the results of an experiment conducted to limit the range of components of carburized steel according to the present invention and the components of the steel material used in this experiment will be explained.

■The composition of the sample steel is shown in the table below.

Composition of test steel (wtlG) ② Carburizing heat treatment was carried out under the three conditions shown in Fig. 2 (a) - (b) and (c).

In addition, C080111g is produced during carburization, and CO is produced during diffusion.

Carburizing treatment was carried out in an atmosphere adjusted to 0.18%.

Figures 3 and 4 are similar to Figures 2 (a), (b), (o
) is a table showing the relationship between the amount of carbon that penetrated from the unit surface of each sample in each carburizing treatment and the amount of 81 and s+p in each sample.

Looking at the table of FIG. 3, the variation is relatively large and not very clear, but it becomes larger as the amount of interstitial carbon 1j81 decreases, and it is recognized that the carburizability deteriorates somewhat due to the increase in the amount of 81.

On the other hand, as shown in the table of FIG. It was found that even a small amount of P significantly inhibits carburizability, and it was found that strict checks on these impurity elements are required to improve rapid carburization.

Among these, the 8 content has a particularly remarkable effect on carburizing properties, so in addition to reducing the 8 content, Mn addition can also increase Fr.
・It is necessary to fix 8.

This can be seen from the influence of No. 8 on the carburizability shown in FIG.

From the above results, 8. The composition of P is P of normal case hardening steel, 8
As mentioned above, it was set lower than the content (about α02%).

[Brief explanation of drawings]

Figure 1 is a table showing the carburizing time and carbon concentration distribution of 8NCM23 steel, Figure 2 (a), (b) - (0) is an explanatory diagram of carburizing heat treatment conditions, and Figure 3 shows the influence of 81 on carburizability. FIG. 4 is a table showing the influence of 8 and P on carburizability, and FIG. 5 is a table showing the influence of 8 on leg immersion. Applicant Komatsu Ltd. Representative Patent Attorney Masaaki Yonehara Patent Attorney Tadashi Hamamoto Distance from the surface of Figure 1 11f lrnm+ yfc (C) //"-m-;-J--1;7=1N
/-1 Figure 3 S content c%) Figure 4 0 0.01 QO20,030,04
S+P content (%) Figure 5 wt%S/wt'/eMn Application No. 57-050170 2, Name of the invention Rapid Carburized Copper 3, Relationship with the case of the person making the amendment Patent applicant address 2-3-6 Akasaka, Minato-ku, Tokyo Name (123)
) Komatsu Ltd. Representative Ryo Kawai - 5, Date of amendment order Voluntary amendment 6, Subject of amendment l Contents of amendment (1) "Steel alloy composition" on page 3, line 5 of specification fIg
Correct it as "steel material composition" ◎ (2) "No.5i, P" on page 3, line 17 of the specification
, J is corrected as "Mn, Si and P, J.

Claims (1)

[Claims] The impurity element 81, P, 8 is 81α05~
α25wt%, po, 05~α015wt1.8α02
~αOI5wt9G 1-Characteristic rapid carburizing steel.