Metallurgical Testing of CMS Crossing ~ MECHTECH GURU

Metallurgical Testing of CMS Crossing

Metallurgical Testing of CMS Crossing

Inspection of CMS crossing shall be carried out in four stages i.e. Stage-I, Stage-II , Stage-III and Stage IV (final stage):-

(i) Stage-I: Inspection shall be carried out after knockout/oxy-cutting/shot blasting etc.

(ii) Stage-II: Inspection shall be carried out after heat treatment and shot blasting etc.

(iii) Stage-III: Inspection shall be carried out after removal/rectification of defects and straightening.

(iv) Stage-IV(Final stage): Inspection shall be carried out after final finishing for final acceptance Out of these four stage of inspection, Stage (II) is done for Metallurgical & Dimensional Inspection for approved vendors.

The testing which are conducted by M&C at stage-II for approved vendor are as follows:-

1. Visual Inspection:

(i) All crossings shall be visually inspected for gross surface defects at various stages of inspection. Dye penetrate methods shall be employed for detection of finer surface defects. Castings thus inspected shall be free from cracks, shrinkage cavities, scabs, flakes, blisters, lack of metal, inclusion, porosities, hot tears, cold shuts and other harmful defects. Minor scattered porosities of less than 4 mm dia and 1.5 mm depth (provided they are not closer than 15mm from each other and not more than three nos. at a particular location) shall be considered acceptable. However, all such defects have to be in a location which is at least 300 mm away from tip of the nose on its either side. Surface of the casting shall be reasonably smooth and free from extraneous matters.

(ii) The crossing shall be free from embedded sand particles and risers, flow off shall be knocked off, ingate at ends and other thick fins, if any, shall be removed by Arc Air or oxy-cut. If oxy-cut, then the cut should be at least 25mm away from the crossing body. The casting shall be suitably shot blasted thereafter, so that they are free from sand etc. and surface inspection can be done visually by the inspecting official without any difficulty. In no case, crossing shall be placed on shaker for removal of sands. Fettling & shot blasting shall be done in such a way so as to avoid any impact to the crossing.

All crossings shall be free from gas pockets, sand holes, cracks, cold shuts and other injurious defects. Lumps and sharp fins, if any, on the edges of the casting shall be suitably removed.

The castings shall bear manufacturer’s identification marks, drawing number, serial number and date of cast. A register shall be maintained by the manufacturer correlating the casting serial number and heat number and register shall be produced to the Inspecting Authority for their verification on demand.

Crossing surfaces/areas/locations i.e. running surfaces, non-running surface, highly stressed locations, nose, wings on either side of nose shall be broadly classified in the following categories depending upon their criticality from the service considerations, for the purpose of repair by welding:

Category-I: 300mm of the top of nose, 300mm of the wings on either side of actual nose of crossing and edges of both top and bottom flanges (upto 25mm from edge).

Category-II: Running surface other than the area mentioned in Category-I.

Category-III: Non-running surface other than the area mentioned in Category-IV and top surface of “Vee” not coming in contact with running wheels of rolling stock.

Category-IV: Non-vulnerable areas like bearing plates, walls of end sections (excluding head portion).

At locations covered in category-I, no casting defects shall be permitted.

At locations covered in Category-II, no rectification shall be allowed on the running surface. Scattered minor defects (excluding cracks) of size less than 4mm dia and upto 1.5mm depth anywhere on this area of the casting shall be left as such, provided these defects are at a minimum distance of 15mm from each other and not more than 3 numbers in a particular location.

At locations covered in Category-III, defects appearing in the crossing surface shall be permitted to be rectified by welding adopting the usual procedure and precautions at the discretion of the inspecting official.

At locations covered in Category-IV, surface defects of size<30mm in diameter and depth <1/3 of thickness may be permitted to be rectified by welding taking necessary precautions and with the knowledge of the inspecting official and to be recorded in the final inspection certificate.



2. Chemical Composition:

One integral test bar shall be detached randomly from any crossing in a melt heat batch. The chemical composition shall be determined by taking sample from the integral test bar so detached which shall represent the entire melt heat batch.

The steel used for crossings, when analyzed as per relevant parts of IS:12308 or any other established instrumental method, shall have the following composition:

Constituent Percent

Carbon 1.0 to1.4%

Silicon(Max) 0.5%

Manganese 11.0 to 14.0%

Sulphur(Max) 0.03%

Phosphorus(Max) 0.06%

The ratio of Manganese to Carbon should be minimum 10 : 1. In case of any dispute, the procedure given in relevant part of IS:12308 shall be the reference method.

Calibration of Spectrometer

Spectrometer should be calibrated at pre-designated intervals based on recommendations of manufacturer/service agency. However, after standardization of spectrometer if wide variation between actual and certified value is obtained for some elements when a certified standard is run, the spectrometer should be calibrated more frequently for those elements.

Wide variation for CMS Crossings will mean:

For Mn 5% of certified value or 0.5 actual variation

For C and Si 5% of certified value or 0.05 actual variation

For P and S 5% of certified value or 0.005 actualvariation

1. Hardness on CMS Crossing:

(a) On every crossing, two location shall be selected at thin and thick section respectively for hardness testing.

(b) The crossing, when tested for hardness by a portable hardness testing method approved by inspecting official, shall have a BrinellHardness number not more than 229 orequivalent.

2. Hardness on Test Bar:

The integral test bar used for impact bend test shall also be selected for making sample for hardness test representing particular melt heat. The sample representing the particular melt heat shall be tested for hardness, in accordance with IS 1500 or the latest adopted revision in vogue and it shall have a Brinell Hardness number not more than 229 or equivalent.

3. Microstructure & Grain Size:

(i) Sample size:-Micro test piece shall be prepared from the integral test bar used for making samples for impact bend test. One test per heat.

(ii) Method of execution and acceptance criterion:-

(a) Grain size of the micro structure of sample shall be 4 or finer as per IS 4748 and it should be single phase austenite, free from Carbide precipitation.

(b) The manufacturer will keep an album of micro-photographs showing ideal structure acceptable structures and unacceptable structures either from literature or from his own heat treated castings. The photographs should be approved by RDSO. Inspecting officials will judge the suitability or acceptability of micro structure with the help of these micro photographs and decision in regard to acceptability shall then be taken.

(c) Software for determination of grain size can also be used. However before use, validation with existing data should be approved by inspecting authority.

4. Impact Bend Test:

(i) Sample size

(a) One test per cast (melt heat) per heat treatment batch shall be carried out on

integral test bars.

(b) The test bar for impact bend test shall have a 30 x 30 mm (tolerance ± 1mm) cross section and be 200mm in length. Four pieces, two from toe end and two from heel end, wherever available shall be taken for this test. Out of these four pieces, two (preferably one from toe end and one from heel end) shall be for the usual acceptance tests and two for any extra tests.

There may be cases where only three test bars are available (e.g. single crossing of particular melt heat and heat treatment batch, one test bar of which has been detached for chemical composition determination earlier). In such case, three pieces shall be taken, out of which two shall be used for usual acceptance test and

balance one piece for retest.

(ii) Execution of Tests:

(a) The impact bend test pieces shall be of un-machined bar, the edges of which may have a chamfer not exceeding 1 mm. Prior to the test, bars shall be notched in a press to a semi-circle (r=1.5mm, depth=1.5mm) on one face at the center across throughout the width in the presence of inspecting official.

(b) The test pieces shall then be placed horizontally on two knife-edge supports spaced 160mm apart, notch downwards and midway between the two supports. The knife edge supports shall have a radius of 2mm. The test pieces must withstand 3 successive blows of a 50 kg weight falling freely from a height of 3m onto the surface opposite the notch. The part of the falling weight coming into contact with the test piece shall be rounded to a radius of 50 mm.

(iii) Acceptance Criteria:

(a) The test pieces must withstand three impacts. They may crack but the crack must not extend more than 7 mmup.

(b) Both test pieces must comply with the above acceptance conditions for the castings of particular melt heat & heat treatment batch to be acceptable.

(c) In case only three test pieces are available for impact bend test, if both test pieces give unsatisfactory results, then castings of particular melt heat & heat treatment batch shall definitely be rejected.

(iv) Extra Tests– Further Heat Treatment

If one (in case of availability of only three test pieces) or one/both (in other cases) impact bend tests give unsatisfactory results, the supplier may opt to request an extra test to be performed.

(a) On the casting as it is.

(b) On the casting after further heat treatment. This, however, shall be possible only on a casting in the unfinished stage.

(c) The extra test shall be carried out on the remaining two/one test piece subject to the same conditions as set out above for the first two tests. If one or both extra tests, gives unsatisfactory results, the castings of particular melt heat &heat treatment batch shall definitely be rejected.

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