DD148963A1 - METHOD FOR MICRO-ALLOYING AUTOMATIC STEEL WITH NON-METAL BORON COMPOUNDS - Google Patents

Abstract

The process according to the invention describes a technology for the microalloying of free-cutting steel with non-metallic boron compounds, in particular with boron-oxygen compounds, such as boron trioxide and / or boric acid. It is the object of the invention to produce boron-alloyed machine steels which, owing to their favorable machining properties, can largely dissipate the corresponding lead-alloyed machine steels. The essence of the invention is that the addition of non-metallic boron compounds at least 90% of the total boron content in the form of acid-boronic boron-oxygen compounds are present, which have a significant positive influence on the Spanungsverhalten in the appropriate distribution.

Description

Title of the invention

Process for the micro-alloying of free-cutting steel with non-metallic boron compounds

Application area of the invention

The invention relates to a process for the microalloying of free-cutting steel with non-metallic boron compounds, in particular with boron-oxygen compounds.

Ch arakter is ik of the known technical solutions

Free-cutting steels are steels which are alloyed with so-called chipbreaker elements to improve machinability on automatic machine tools. These elements are virtually insoluble in the steel matrix and deposit as inclusions in the steel. «

Due to the interruption of the metallic base material, the chips break off during the machining process. In addition, the cutting force is reduced. These steels are therefore particularly suitable for machining on automatic machine tools and enable high metal removal rates. The chipbreaker elements are primarily sulfur. In addition, better machinability is achievable if lead is alloyed as a chipbreaker element in accordance with US Patent Specification Nos. 2182,785, 2197,259 and 2259,342.

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The highest cutting performance can be achieved if sulfur-lead-alloyed steels additionally alloyed with bismuth, selenium and tellurium according to the invention specifications FR-PS 1 219 601, GB-PS 1 020 423 and US-PS 3,152,890.

The alloying elements mentioned, except sulfur, have the disadvantage that during the alloying, hot forming and heat treatment process of the steel toxic vapors arise. Despite the use of suction devices, the permissible levels of these elements or their compounds in the ambient air at the workplaces in metallurgy are often exceeded, whereby production restrictions in the production of these steels are unavoidable.

The addition of micro-alloying elements is known primarily for improving the mechanical properties of construction, insert and tempering steels.

US Patent Specification Nos. 2,388,214 and 2,388,215 mention the micro-alloying of free cutting steel with boron to improve machinability, with the addition of boron in the form of ferroboron with a boron content of 10 to 20 percent by mass. Also, the DL-PS 129 664 describes a boron micro-alloyed V / eich-free cutting steel with a higher sulfur content, wherein the alloying of the liquid steel is carried out with boron in the ladle.

The above-described descriptions of the prior art have the metallurgical and procedural disadvantage that no sufficient statements are made about the nature of the manufacturing and alloy technology with regard to securing the service properties of free-cutting steels.

Object of the invention

The object of the invention is that a boron microalloyed free cutting steel is produced without toxic side effects, which has better cutting properties than the sulfur alloyed free cutting steel and can replace the lead alloyed free cutting steel.

Explanation of the essence of the invention

The invention is based on the object that improved by a suitable alloying process, the machinability of sulfur-alloyed free-cutting steels by using non-metallic boron compounds and thus the performance characteristics of the known sulfur-lead-alloyed free cutting steel is approximately achieved.

According to the invention, this object is achieved in that a molten steel in addition to the usual for sulfur-coated free-cutting steels alloying non-metallic boron compounds, in particular boron-oxygen compounds in an amount up to 3.0 kg per ton of steel, preferably in an amount of 1.0 to 2 , 0 kg per ton of steel in a melting unit and / or in a tapping channel and / or in a steel pan and / or in a mold and / or in a distribution vessel are added.

The process according to the invention ensures that total boron contents of 30 to 160 ppm are achieved with an acid-soluble fraction of the total boron content of at least 90 % .

It has been found that the phases which have the effect of machining must be present as boron-oxygen compounds. Just add it to the hot ladle before tapping and / or during tapping into the tapping tray or into the tapping tray

Ladle comes boron trioxide or boric acid of any grain size, preferably with a diameter of 10 to 50 mm in question. With simple gravity addition in the mold and / or in the pouring stream is boron or boric acid any grain, preferably with a diameter of 5 to 20 mm in terms used to prevent dust nuisance.

To improve the Legierungsausbringens and the homogeneity of the addition of boron trioxide or boric acid in powder form of any desired grain size must, preferably with a diameter of 60 to 500 / um by means of the injection device into the steel of the ladle and / or into a distribution vessel and / or in a mold and / or in a pouring stream.

Ausführungsbei game1

The invention will be explained below with reference to two embodiments.

1 · After the blowing process, the temperature of the steel bath in a bottom-blowing oxygen converter is 1983 K with the following chemical composition:

0.020 mass% of carbon

Trace silicon 0.190 mass% manganese 0.043 mass% phosphorus 0.018 mass% sulfur.

After the slagging, the melt is pre-deoxidized with 11.8 kg of ferromanganese carburic acid per ton of steel in the converter. Ten minutes before tapping, 1.8 kg of lumpy boron trioxide per ton of steel are added to a hot ladle. When tapping into the pan each .Tonne steel

7.1 kg perromanganese carbure (finely divided)

3.1 kg of sulfur blossom

1.2 kg refining agent

added.

The achieved persistence analysis of

0.1000 mass% carbon 0.0200 mass% silicon 1.100 mass% manganese 0.0620 mass% phosphorus O ,, 316O mass% sulfur 0.0040 mass% nitrogen 0.0076 mass% boron (acid-soluble)

is within the target analysis range of the steel brand 9SMnB28.

2 · In a bottom-blowing oxygen converter, the temperature of the steel bath after the blowing process is 1973 K with the following chemical composition:

0.040 mass% of carbon

Trace silicon 0.250 mass% manganese 0.047 mass% phosphorus 0.020 mass% sulfur.

After slagging, the melt is pre-deoxidized with 7.9 kg of perromanganese carbide per tonne of steel. When tapping into the pan per ton of steel

11.0 kg perromanganese carbure *

(fine) 3.7 kg sulfur bloom

1.2 kg of refining agent added *

At a pouring temperature of 1853 K, 2 kg of boric acid (H "BO") per tonne of steel is alloyed with powder in the pouring stream from the start of casting to 2/3 mold filling. "This produces the following final analysis corresponding to the 9SMnB28 steel brand:

0.1100 mass% of carbon 0.0200 mass% of silicon 1.0400 mass% of manganese

0.0420 mass% phosphorus 0.2510 mass% sulfur 0.0050 mass% nitrogen 0.0046 mass% boron (acid soluble).

The improvement of the machinability of free-cutting steel which has been micro-alloyed with boron by the described methods can be demonstrated by a complex short-test method. The measured average yield values ν and the average roughness values Ra of the sample batches determined by the cutting speed increase method differ significantly from the averages of the base steel grade 9SMn28 (Table 1).

Table 1: Results in the measurement of the seasonal cutting speed v_ and the average roughness Ra (turning)

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Steel brand remark ν / * "m. Min" J Ra Γΐι in 7

9SMn28 Stahlmarken- 129 2.04 Average 9SMnB28 1st example 145 1.74 charge 9SMnB28 2e example 148 1.48 charge

Claims (4)

invention claim 1. A method for microalloying free cutting steel with non-metallic boron compounds, in particular with boron-oxygen compounds, characterized in that the boron-oxygen compounds of a molten steel in a melter and / or in a tapping channel and / or in a steel pan and / or in a mold and / or in a distribution vessel in an amount up to 3.0 kg per tonne of steel, preferably in an amount of 1.0 to 2.0 kg per ton of steel to achieve a Gesamtborgehaltes in steel from 30 to 160 ppm at a acid-soluble proportion of at least 90 % of the total boron content are added. 2. The method according to item 1, characterized in that as boron-oxygen compounds boron trioxide and / or boric acid of any grain size, preferably with a diameter of 10 to 50 mm before tapping into a hot ladle and / or tapping the molten steel in the Tapping gutter and / or be added to the ladle. 3. The method according to item 1, characterized in that the boron trioxide and / or boric acid in any grain, preferably added with a diameter of 5 to 20 mm by gravity into the mold and / or falling or rising casting and continuous casting the pouring stream v / ground. 4 «method according to item 1, characterized in that the boron trioxide and / or boric acid in powder form of any grain, preferably with a diameter of 60 to 500 / um by means of an injection device of known type in the steel bath of the ladle and / or in the distribution vessel and / or be blown into a mold and / or into a pouring stream «