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Non quenched and tempered steel and manufacturing process thereof

a technology of tempered steel and quenching process, which is applied in the direction of heat treatment process control, metal rolling arrangement, metal-working apparatus, etc., can solve the problems of not meeting the energy-saving and environmental protection requirements at present, bringing some waste product loss, and high cost of quenching and tempering process, so as to avoid the disadvantageous effect of large hardness changes on cutting tools and processing, and effectively avoiding defects

Inactive Publication Date: 2016-08-11
PEKING UNIV FOUNDER GRP CO LTD +2
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention provides a process for producing non quenched and tempered steel with improved mechanical properties and production efficiency. The process involves a cooling control after finish rolling, which includes alternate intense cooling and moderate cooling to achieve uniform mechanical properties and improve production efficiency. The use of shield cooling after air cooling allows for a slower cooling speed, resulting in improved overall mechanical properties.

Problems solved by technology

Quenching and tempering processes are high in cost.
Since quenching and tempering processes increase energy consumption, pollute the environment, and bring some waste product loss, they do not meet the energy-saving and environmental protection requirements at present.
The difficulty of such process in production is the control of steel performance.
However, as shown by studies, it is difficult to make non quenched and tempered steels achieve performance requirements only by component design.
The non quenched and tempered steels produced by above process are difficult to ensure the core temperature and the surface temperature of the steels to become the same by slow cooling within a short time, and tend to cause the surface and core of the steels have large differences in strength and toughness, and seriously nonuniform mechanical properties.

Method used

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  • Non quenched and tempered steel and manufacturing process thereof

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0053]This example provides a process of producing non quenched and tempered steel, comprising a finish rolling step and a cooling step after the finish rolling, wherein, in the finish rolling step, the temperature of rods at the entry into the finish rolling step was controlled at ≦850° C.; the rods were subjected to low temperature rolling when the rods temperature is 850° C.-900° C. After the rolling, the steel was subjected to three stages of water cooling by means of a specialized controllable water cooling unit, wherein the first stage of water cooling employed intense cooling, the second stage of water cooling employed moderate cooling, and the third stage of water cooling employed intense cooling.

[0054]Here, it should be noted that there are many ways to control water cooling intensity. In this example, the water flow was controlled by controlling the opening degree of the valve(s) of water cooling unit so as to control water cooling strength. Specifically, the first stage v...

example 2

[0056]This example provides a process of producing non quenched and tempered steel, which was a further improvement over Example 1. As compared with Example 1, this process further comprises a smelting step before the finish rolling step, the smelting step comprising electric furnace smelting step, ladle furnace smelting and refining step carried out sequentially.

[0057]In the electric furnace smelting step, molten iron smelting was employed, the phosphorus content before steel tapping was strictly controlled at ≦0.015%, the final carbon content was 0.03% to 0.10%, and the final temperature was 1670° C.-1700° C. The electric furnace smelting can better control deslagging operation than traditional converter smelting.

[0058]In the ladle furnace (LF) smelting step, deoxidization was performed using silicon carbide, ferrosilicon powder; lime was added to make white slag; the white slag was held for 20 minutes or more so that the inclusions can be thoroughly removed by the white slag.

[005...

example 3

[0061]This example provides a process for producing non quenched and tempered steel, which was a further improvement over Example 1 or 2. In this example, the continuous casting step and heating step were improved. The continuous casting step and the heating step were arranged after the refining step, and before the rolling step and the water cooling step.

[0062]In the continuous casting step, molten iron in a tundish was introduced into a crystallizer by a submerged nozzle, thus the problem that air tends to be brought in when using traditional nozzles is avoided. Furthermore, argon gas was blow to the joint site of the submerged nozzle and the tundish, thus preventing air from entering into the tundish. The overheat was strictly controlled at 23-35° C., and the pulling speed was controlled at 0.5 m / min-0.6 m / min. In the continuous casting, low overheat and low casting speed ensured the quality of casting blank. When cutting after continuous casting, the temperature at cut place was...

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Abstract

A non quenched and tempered steel and manufacturing process thereof. The process comprises a cooling step after the finish rolling step; and the process utilizes alternate intense cooling and moderate cooling. The intense cooling can ensure the surface temperature of the steel to decrease rapidly; and the moderate cooling allows the core temperature of the steel to dissipate gradually to the surface; a further intense cooling is carried out to allow rapid heat dissipation. The intense cooling and the moderate cooling can be carried out alternately several times according to practical requirement. A water cooling mode combining intense cooling and moderate cooling allows the core temperature and the surface temperature of the steel to become the same within a short time, and thus ensures the uniformity of the mechanical properties of the steel and improves the production efficiency.

Description

TECHNICAL FIELD[0001]The present invention relates to a non quenched and tempered steel and its manufacturing process, and belongs to the technical field of ferrous metallurgy.BACKGROUND[0002]Currently, bars for machine cutting in China generally use ordinary steels, such as 45, 40Cr and 42CrMo steels. These bars need quenching and tempering heat treatment when used as raw materials for machine cutting. Quenching and tempering processes are high in cost. Since quenching and tempering processes increase energy consumption, pollute the environment, and bring some waste product loss, they do not meet the energy-saving and environmental protection requirements at present. Therefore, non quenched and tempered steels that do not require quenching and tempering processes and can be directly used for cutting will gradually replace ordinary steels and become a trend in the future. Non quenched and tempered steels means mechanical structural steels that can achieve performance requirements wi...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C21D9/52C22C38/46C22C38/42C22C38/06C22C38/04C21D9/00C22C38/00C22C33/04C21D8/06C21D6/00C21D1/667C21D1/60C22C38/58C22C38/02
CPCB21B37/74C21D1/60C22C38/16C22C38/46C22C38/58C21D8/0231C21D8/065C21D9/0062C21D11/005C21D1/667C21D2211/005C21D2211/009C22C38/42C22C38/04C22C38/02C22C38/002C22C38/001C22C33/04C22C38/06C21D9/525C21D6/008C21D6/005C21D6/004B21B45/02B21B1/46B21B37/76B22D11/001
Inventor LIU, DONGLINZHOU, XUXU, YIFENGZHOU, ZHIWEIYU, JIE
Owner PEKING UNIV FOUNDER GRP CO LTD
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